A knife crime charity said the figures show the justice system is not working as a deterrent or as a means for rehabilitating offenders.
New figures released by the Ministry of Justice show 17 of the 85 convictions recorded by Dyfed-Powys Police for possession of an article with a blade or point in the year to September led to a suspended sentence.
It meant suspended sentences made up 20% of convictions – down from 26% the year before, but up from 8% a decade ago.
Across England and Wales, the number of suspended sentences handed to people convicted of possessing a knife has reached its second highest point in a decade, while the number of total convictions remained stable.
A total of 4,303 suspended sentences were issued for possession offences in the year to September – up from 4,144 in the previous 12 months and a significant increase on the 2,347 in the year ending September 2014.
These accounted for 25% of all convictions for possession.
The figures come as ministers announced a raft of anti-knife crime measures to tackle the supply of knives online.
Patrick Green, CEO of the Ben Kinsella Trust, said there was a "severe disconnect" between the severity of knife crime and justice for victims.
He added: "It begs the question: how can we effectively address knife crime when the very system meant to deter and punish offenders appears to be under such immense strain?
"This data shows that the current system is not working, either as a deterrent or by providing the necessary rehabilitation to reduce reoffending."
In Dyfed and Powys, 21 of those caught with a knife received an immediate prison sentence – accounting for 25% of convictions.
Of the rest, 14 received a community sentence, and 26 were cautioned.
A government spokesperson said sentencing in individual cases was a matter for the independent judiciary, which has "has a broad range of sentencing powers to deal effectively and appropriately with offenders".
They added: "We will pursue every avenue to protect young people.
"This is why we are bringing in Ronan’s Law to stop knives from being sold illegally online, why we have banned zombie style knives and machetes and why we are delivering 13,000 new neighbourhood police officers to make our communities safer.
"But young people must also be supported so we are developing a Young Futures programme to intervene earlier to steer children away from falling into crime."