A Supreme Court judge has ordered a new trial for the man accused of murdering five members of the same family in Sydney.

Discharging the jury, the judge said new evidence had emerged late last month which may make a substantial difference to the trial of Robert Xie.

Xie was accused of creeping into the home of his brother-in-law Norman Lin and sister-in-law Lily Lin in North Epping in the early hours of July 18, 2009.

Prosecutors alleged that Xie, motivated by bitterness, killed Lin, Lin's wife Lily, the couple's two sons Henry, 12, and Terry, nine, and Lily's sister Irene, with a hammer-like weapon.

Xie pleaded not guilty to the murders.

Justice Peter Johnson said the new material presented may change the shape and content of the trial in significant ways.

He told the court the defence had requested the jury be discharged, and the Crown had agreed, and he believed it was the appropriate course of action.

He told the jury they were discharged and there would be a new trial with a new jury, which is expected to start on July 21.

Justice Johnson congratulated them for their hard work and said all the notes they had taken would be destroyed.

During the trial, the court heard Xie had been criticised by his father-in-law for not having a job and suffered a loss of face that motivated him to murder five family members.

Yang Fei Lin, father of Norman Lin, gave evidence that by the end of 2009, a dispute had broken out about the guardianship of the surviving member of the family and the assets of Norman.

In this argument, Mr Lin said Xie "got really angry", and questioned why he would not give any of the inheritance to his wife and Mr Lin's daughter, Kathy.

However, Xie's barrister said aspects of the Crown case against his client were "pure speculation" and "assumption".

Xie's barrister, Graham Turnbull SC, told the court some Crown witnesses who were to give evidence at the trial were not questioned by police for months, even years after the killings his client was accused of.