The chair of the royal commission into child sex abuse is calling for legal changes to help victims, saying in a speech to be delivered today that while the number of cases before the courts has almost doubled in recent years, conviction rates are down and the number of acquittals has risen.

Justice Peter McClellan is calling for changes to legal processes and the rules of evidence to ensure victims are given the best chance of receiving justice.

In a speech to be delivered to a conference in Sydney today, Justice McClellan said the work of the Royal Commission into Institutional Responses to Child Sexual Abuse had seen many more victims coming forward to police.

But official data shows conviction rates are down and the chances of an offender being acquitted have risen rather than fallen.

Justice McClellan said some victims who had been through the process of a criminal trial had spoken of the trauma involved in giving evidence, with some characterising it as "as bad as the abuse itself".

He says it was increasingly apparent there needed to be changes to the way evidence was admitted in court to ensure the system achieved justice "not only for the accused, but also for victims".

The New South Wales Office of the Director of Public Prosecutions is hosting the conference, aimed at understanding what government and non-government agencies can do to best support victims through the legal process.

Speakers include DPP Lloyd Babb SC, victims' advocates Rebecca Poulson and Sascha Chandler and Crown Prosecutor Gina O'Rourke SC.