The rate of successful rape convictions in 2020 was the lowest for more than 10 years.
The latest figures from the Ministry of Justice showed 31 per cent of all people charged with rape were convicted (89 people).
For all sexual offences, the conviction rate was slightly higher, at 44 per cent.
But that is still far below the conviction rate for other charges, which stood at 71 per cent.
Women's Refuge chief executive Dr Ang Jury said the data showed it's still too easy for people who are charged to escape conviction.
"If you are charged with a sexual or a family violence offence, you've got a fairly good roll of the dice of getting away with it. That's what these numbers say.
"If the consequences aren't there, then nothing is going to change."
She said it's even more concerning, given the police only bring charges against people if they think they're likely to get a successful conviction.
Jury said it showed the Ministry of Justice's current approach is not working.
"People are being charged, people are appearing in court, but judges are not convicting.
"Where the fault actually lies, is a little bit hard to tell. But it appears the victim focus isn't getting the cut-through it needs at the moment."
She said better education was needed so juries could make informed decisions.
"People need to start better understanding what it actually is they're dealing with, starting to get rid of some of those myths, and all those old-fashioned ideas that really just keep sticking around."
Last year a survey commissioned by the Ministry of Justice found 94 per cent of sexual assaults aren't even reported.
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 charges increased by eight per cent last year, despite a decrease of one percent for overall crime.
These offences included a number of crimes such as domestic assault, sexual violence against a spouse and coercion to marry.
More than a quarter of people convicted for family violence offences went to prison, while a further 60 per cent received a community sentence such as home detention or intensive supervision.
Green Party co-leader Marama Davidson said the increase in family violence offences did not come as a shock and the the added stress of the Covid-19 pandemic and economic pressure may have contributed to the spike.
Davidson said another possible reason could be increasing trust in the system, meaning more women were reporting crimes which previously have been unreported.
But she said a focus on prevention had failed to bring the number of offences down and systematic change was needed.
A domestic violence service provider says an increase in family violence offences cannot solely be blamed on the pandemic.
Shine advocate team manager Debbs Murray said New Zealand had a domestic violence epidemic long before Covid-19.
"When you're looking at second level entrapment, so you're dealing with victims who are already trapped in relationships in which they're unable to move, and suddenly also physically trapped in an environment where they're unable to move, there is going to be an increase in family violence and severity for people who have already got a propensity to behave that way."
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.