Figures released by the Conservatives show the number of inmates sentenced to four years or less who automatically qualify for release after serving half their time went up by almost 4% in 2012 compared to 2011.
The early-release scheme will also see a range of criminals on longer sentences freed after serving two-thirds of their sentence, including 38 people convicted of rape or attempted rape and 81 convicted of homicide.
More than 3300 people sentenced for attempted murder or serious assault will also be able to leave jail early on parole.
Scottish Conservative justice spokesman David McLetchie MSP condemned the SNP for failing to end the early-release scheme, as promised in the party's election manifesto, and said it showed ministers were "soft on justice."
But Justice Secretary Kenny MacAskill accused the Tories of "rank hypocrisy", saying the party was behind the move to introduce automatic early release before devolution.
A total of 15,312 criminals sentenced in 2011/12 will be released early in the future, 3.8% more than the previous year.
Mr McLetchie said: "Far from being scrapped, this disastrous policy is actually benefiting more dangerous criminals as time goes on. When convicts – especially those guilty of serious crimes – are handed down a sentence, the public expects that to be served.
"Instead, what we have is people who have committed murder and rape walking free half or two-thirds of the way through. It is no wonder the SNP is accused of being soft on justice when it refuses to drop such a discredited policy."
Mr MacAskill's spokesman said: "This is rank hypocrisy from the Tories on two counts – they are the ones who brought in automatic early release, and they have also tried to block its scrapping by objecting to the presumption against short prison sentences, which will make sure jail is for serious criminals.
"This Government has delivered a 37-year low in recorded crime, helped by the 1000-plus extra police officers we have recruited – at the same time as thousands of police jobs are being cut by the Tories south of the Border."
A Scottish Government spokeswoman said it remained committed to ending the early release scheme when it was "feasible". She said: "Prison must be used for locking up serious and dangerous criminals and keeping them off our streets but it is clear that we can't keep packing more and more low-level prisoners into our jails and giving them free bed and board."