Paris prosecutor Remy Heitz said any police involved in violent acts against Yellow Vest protesters would end up in court by the end of the year.
"I want to be clear: there is no desire on my part to downplay this violence or to minimise it," Mr Heitz told Le Parisien on Thursday.
The French authorities have been criticised for their handling of the protests, which began last November and have continued every Saturday since.
There has been a series of very violent clashes between Yellow Vest demonstrators and police, especially in Paris, sparking complaints that the police have been heavy handed and too ready to use tear gas and rubber bullets.
Mr Heitz said there had been more than 170 cases of police violence reviewed, with 57 of them completed and awaiting a decision whether to prosecute.
Judicial sources said eight cases have been handed over to investigating magistrates.
Mr Heitz raised the specific cases of Jerome Rodrigues, who lost an eye in a March 26 demonstration, and another of an incident in a Burger King outlet in December where police fired rubber bullets.
But for the moment no police were being investigated, he said, while promising there would be action.
Mr Heitz said that on the other side, more than 2,900 demonstrators had been detained for questioning since November, with no action taken in 45 per cent of the cases.
Investigations continue in 30 cases, which were "the most complex and serious of aggression against security personnel, theft of luxury goods signs or damage to the Arc de Triomphe", he said.