For all sexual offences, the conviction rate was slightly higher, at 44 per cent.
The conviction rate for other types of charges is 71 per cent.
Ten-fold funding boost needed - RespectEd
RespectEd Aotearoa chief executive Fiona McNamara said the statistic showed the system for dealing with sexual violence was not working and systemic change was needed.
She said Government spending on prevention needed to be boosted more than 10-fold.
"There has not been a focus on prevention - there is very little happening. There are some initiatives going on but not enough.
"The Government spend on prevention is extremely low compared to what is spent after a crime has happened.
"We want to stop sexual harm before it happens."
McNamara said sexual violence was poorly understood in the community and the statistics appeared to show it was the same for juries, judges and lawyers.
She said more education was needed.
"We need to continue to grow that understanding and continue to develop people's understanding about how sexual harm can play out, what barriers there are for survivors.
"Things like why it might have taken them a lot of time to report, or why a story might change somewhat throughout a [court] process because of the effects of trauma and how that can harm someone and how it can affect the way that they tell their story."
Family violence at 5-year high
Other systemic changes needed included more resources for survivors of sexual harm, and to treat perpetrators.
McNamara said events like last week's rally against sexual violence in Wellington, and the MeToo movement, felt like positive steps in the community's understanding of sexual harm.
"All these movements where survivors are speaking and people are ready to talk about this issue and society is becoming less and less tolerant of it and more able to recognise sexual harm happening.
"If that is not translating into convictions in court then it shows ... the system is broken."
She said the Sexual Violence Legislation Bill in Parliament includes changes that would improve the system and outcomes for survivors.
The Crime and Victims Survey data also showed family violence offences were at a five-year high, with more than 30,000 recorded in 2020.
Family violence offences increased by 8 per cent last year, despite a decrease of 1per cent for overall crime.
- RNZ
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334.
• Alternatively contact your local police station
• If you have been abused, remember it's not your fault.
