A woman's sexual history or how she dresses will be out of bounds in future court cases under a raft of reforms designed to protect victims from being unfairly treated and retraumatised.

Such information, called "rape myths" by survivor advocacy groups, will only be admissible in a court if the judge deems it should be, and if not doing so would impede the course of justice.

The new rules about rape cases in court are contained in the Sexual Violence Legislation bill, passed its first reading in Parliament today and is expected to become law early next year.

The bill seeks to maintain fair trial rights while improving the court experience, which complainants have described as retraumatising, hostile, and a compelling factor in deterring victims from coming forward at all.

An estimated one in four women and one in seven people experience sexual violence in their lifetime, but most cases are unreported, and of those reported to police, only a third go to court and one in 10 end in convictions.

Justice Minister Andrew Little said he hoped the bill would eventually encourage more complainants to come forward, though it was difficult to say if it would have any effect on conviction rates.

The bill would:

• See more alternative ways to give evidence - such as via video conference or in a cleared courtroom - to protect complainants appearing in front of the accused or the accused's supporters.

• Protect complainants from unduly invasive questioning, such as questions about sexual history or choice of clothing; relevant details would be established before a complainant is questioned. A judge would also be required to direct the jury to ignore rape myths.

• Require a judge to intervene in inappropriate lines of questioning, such as ones that are improper, unfair, misleading, or needlessly repetitive.

• Allow a survivor to give an victim impact statement to a courtroom cleared of the public.

Justice Under-Secretary and Green MP Jan Logie said the myths about rape - including sexual history and a complainant's choice of clothing - unduly influenced court cases.

"You can consent to sexual activity with somebody at a particular time and not at another. Consenting the first time does not automatically [mean] you have consented the second time. Choice matters."

Chief Victims' Adviser Kim McGregor said that cross-examination was the most destructive and distressing part of the court process, and better protections for complainants were long overdue.

"I have heard from those who feel broken, humiliated and worn down after hours and sometimes days of repeated questioning."

She said complainants accepted that evidence needed to be tested, but will welcome the changes in the bill that would disarm the process of hostility.

Allowing victims to have their evidence recorded would also lessen delays in giving evidence, allowing them to move on with their lives sooner.

"It should reduce the retraumatisation and enhance their sense of fairness."

Wellington Women Lawyers' Association convener Steph Dyhrberg said it was important to require judges to direct juries about the misconceptions around rape.

"The general public is remarkably ill-informed about the realities of sexual violence and how survivors experience it and behave. Those assumptions and prejudices and misinformation, jurors take into the courtroom and jury room."

This was echoed by Wellington Rape Crisis agency manager Kyla Rayner.

"We don't want to see the continuation of discrediting survivors' experiences or colouring outcomes with rape myths."

Questions to witnesses should be respectful, relevant and fair, and she said it was appropriate to require a judge to intervene when questions were improper, or even harmful.

Wellington Sexual Abuse Help foundation chief executive Conor Twyford said a person's sexual disposition should never be considered as evidence against them.

"Survivors have a right not to have their sexual history used against them, full stop.

"A person's prior sexual activity should have no bearing on the case at hand."

Logie said the bill was the first phase of change.

The second stage would look at the nature of consent, the role of juries, and alternative process including an inquisitorial system that, for example, focuses more on fact-finding than challenging evidence under cross-examination.

She said the current system was so poor at the moment that people working in the system have said they wouldn't advise their own family members to lay complaints.

"What they saw was the system making it harder for people."