Nearly 250 people in Wales reported suspected stalkers to police between 2012 and 2015, the Network for Surviving Stalking said.
The charity is providing training for the police.
It said 76% of women murdered by ex-partners had been stalked by them.
It is because of this the Network for Surviving Stalking is launching an awareness campaign to help people identify stalking behaviour before ex-partners become violent.
Assia Newton, 45, from Pencoed, Bridgend county, was murdered by her estranged husband Kelvin Newton in 2013.
Her sister, Nadia Salaman, told BBC Wales she believes Assia might still be alive if his behaviour had been identified as stalking at the time.
Mrs Salaman said Newton was constantly turning up unannounced and making her sister feel uncomfortable: "Eight o'clock every morning he was going there, he said he was going there to make my sister a cup of tea and take it to her in bed, because he was letting himself in.
"She said she didn't want him up there.
"If maybe he had been arrested, it would have given my sister some breathing space, who knows what would have happened?"
Stalking became a specific criminal offence in Wales and England in 2012.
According to the charity, 246 people in Wales reported suspected stalkers to police between November 2012 and April 2015. During that period 93 people were charged.
Across the UK, one in six women and one in 12 men will be stalked in their lifetime and many will not contact the police until there have been 100 incidents.
Gwent Police officers will receive training from Network for Surviving Stalking and watch a film called Trouble With an Ex, produced by the charity and funded by Gwent's police and crime commissioner.
The force has previously been criticised for its handling of a number of murders of women killed by their partners or ex-partners.
Gwent Police officers are to become the first in England and Wales to be trained on the danger posed by people who stalk their ex-partners.