A midnight driver who barrel-rolled in a horrific 200km/h smash that killed his new partner has today pleaded guilty.

Jaimey Leigh Fellows, 32, died when her partner of three months, Craig Richard Bennett, lost control at high speed on State Highway 1, near Burnham, 30km south of Christchurch, in the early hours of October 21 last year.

At Christchurch District Court this afternoon, Bennett, of Dunsandel, admitted a charge of dangerous driving causing her death.

The court heard how the couple were travelling in Bennett's Nissan south of Rolleston when he started picking up speed.

He overtook a delivery truck on double lines and sped past another car on a passing lane near Burnham Military Camp.

But as he attempted to exit the passing lane, he lost control. Crash investigators found Bennett was doing between 200-204km/h.

Police prosecutor sergeant Paul Scott said Bennett couldn't regain control as the car crossed the centreline.

The passenger door smashed through a fencepost and the car began to barrel-roll, the court heard.

Fellows' seatbelt snapped and she was ejected in the final barrel-roll as the car came to rest near the railway track, some 200m from where the crash began.

She died as a direct result of high-energy impact injuries to her chest, abdomen and limbs, the court heard.

Bennett later tested positive for THC, the active constituent for the drug cannabis.

He admitted to police that he had been the driver but had limited recollection of events.

Defence counsel Andrew McCormick said Bennett, who is still recovering from his own crash injuries and not yet back at work, would willingly participate in a restorative justice conference.

Judge Barbara Morris referred the case to be considered for restorative justice and remanded Bennett on bail ahead of sentencing on August 29.