Victim advocates are increasingly worried about the lower number of trials, which they say shows an urgent need for sexual assault law reforms in the territory.

ACT Attorney-General Shane Rattenbury has promised work will start on reforms to offer better support to victim-survivors.

There were 230 sexual offence trials in the ACT in the five years from 2010-11 to 2014-15, according to figures in ACT Director of Public Prosecutions annual reports.

But in the following five years there were just 105 trials. This was despite 2667 reports of sexual offences to police during this period, according to figures from the recent ACT Policing annual report.

The conviction rate has also fallen in that time. In the first five-year period there was a guilty verdict in 59 per cent of trials, whereas in the past five years there was a guilty verdict in 55 per cent of cases.

That is despite victim support services reporting a surge in demand.

Calls to the Canberra Rape Crisis Centre crisis line have soared. In 2011-12 the centre received 8911 crisis calls, but in 2019-20 it fielded 25,848 calls.

At Victim Support ACT there has been a 304 per cent increase in the provision of hours needed for sexual assault counselling, from 486 hours in 2016-17 to 1964 hours in 2020-21.

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As well, ACT Policing crime statistics show a 57 per cent increase in the number of sex offences reported over five years, from 384 reports in 2014 to 606 reports in 2019. However, the number of reports did drop in 2020 to 449.

Canberra Rape Crisis Centre chief executive Chrystina Stanford said the burden of proof needed for victims was too high.

"If a matter is not proceeding, that doesn't mean something didn't happen, that doesn't mean that the person wasn't sexually assaulted," she said.

"But if the evidence needed is ... at a really high level it does automatically mean that a number of people couldn't proceed."

Mr Rattenbury said the data reinforced what the government had heard from advocates, and the government would work to restart its sexual assault law reform program.

"Reports to police are increasing, but so are the attrition rates, where survivors don't proceed with a formal charge or where they withdraw partway through," he said. "It is important for us to understand exactly why that is, so we can ensure those who come forward to report their lived experience of sexual assault, harassment or abuse are supported."

ACT Director of Public Prosecutions Shane Drumgold was cautious in his assessment of the trial data.

"There will always be variations in both the number of trials and conviction rates from year to year, so one needs to approach randomly selected years with caution," he said.

Mr Drumgold said the average conviction rate for sexual assaults in the ACT over the past 10 years is 57.3 per cent and the average number of yearly trials is 33.

He said from year to year there may be a lower number of trials, and the coronavirus pandemic had impacted the number of trials in 2019-20.

The ACT government's sexual assault law reform program will work with experts and stakeholders who will help to identify and implement reforms to sexual assault processes.

Victims of crime commissioner Heidi Yates will be among those to play a role in the program.

"We need to understand where matters are dropping out of the system, from initial report to failure to proceed to prosecution," she said. "There's a very high number of matters where legal action isn't taken, because the matter is considered unfounded. We actually need to know more about what's happening when police choose not to proceed and why."

Mr Drumgold said he considered the flagged reform work by the ACT government as a continuation of reforms that began in 2005.

"In my view, 15 years of sexual assault law reform in the ACT and around Australia has largely focused on the protection of sexual assault victims, particularly focusing on their interaction with the criminal justice system, and has been very successful," he said.