North Wales Police had 473 complaints in 2014/15 - a 43% rise on the previous year - Independent Police Complaints Commission figures (IPCC) show.
Gwent Police had 398 complaints - up 28 - and South Wales Police saw a 20% rise to 864. But Dyfed-Powys had 268 complaints - a decrease of 18%.
There were record number of complaints against police in England and Wales.
A total of 37,105 complaint cases were recorded in 2014-15 - a 6% rise in the amount of complaints made in 2013-14.
The most common complaint made was for "neglect or failure in duty".
In Wales, the number of complaints in the last five years have increased at a slightly higher rate than the increase nationally.
Compared to 2009/10, the number of complaint cases recorded by Welsh forces in 2014/15 increased by 10%. Over England and Wales as a whole the increase was 8%.
The figures found:
The IPCC said the figures also revealed "marked inconsistencies" in whether forces investigated most complaints formally, or used more informal "local resolution" processes.
Dame Anne Owers, chairwoman of the IPCC, said overall the figures showed a complaints system that was "both over-complex and inconsistent, and is clearly failing to satisfy a significant number of complainants".
She said: "Chief officers and police and crime commissioners should look closely at the figures for their own forces to satisfy themselves that complainants are being treated fairly and well.
"However, the underlying problem is the system itself. We welcome the fact that the government proposes to bring in legislation to simplify and streamline a system that at present satisfies neither those who need it nor those who have to operate it."
The number of complaints made to the watchdog marks the most it has received since it started collecting data in 2004-05.
Det Supt Richard Lewis, Dyfed-Powys Police's head of professional standards department, welcomed the reduction in complaints, adding: "It is important to us that people have the confidence to report complaints, and know that we have a thorough procedure for investigating and monitoring complaints."

Mourners stopped in ones and twos by the building on the Rue Nicolas-Appert, where a plaque was unveiled on Tuesday.
Seventeen people died in January last year when gunmen targeted the magazine and a Jewish supermarket.
No official events are planned for Thursday, although President Francois Hollande is due to address the police.
Marine Le Pen, the leader of France's far-right opposition party Front National, is also expected to speak at some point during the day.
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As well as the memorial at the magazine's former office, a second plaque was installed where a police officer was shot, and a third at the Jewish supermarket.
On Saturday, a fourth plaque will be unveiled in the southern suburb of Montrouge, where one of the gunmen shot a policewoman.
The commemorations will culminate in a public event on Sunday in the Place de la Republique, where Parisians gathered in the wake of the attacks.
A 35ft (10m) oak "remembrance tree" will be planted in the square and veteran French musician Johnny Hallyday will perform Un Dimanche de Janvier (One January Sunday), a song recalling the vast march in Paris that followed the attacks.
Amid the commemorations, Charlie Hebdo has once again courted controversy with the cover of its special anniversary edition. It depicts God, bloodied and carrying a gun under the headline "One year on: The assassin still at large".
Three Welsh police forces have seen huge rises in the number of complaints they received last year.
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Parisians have laid flowers and lit candles at the former office of Charlie Hebdo ahead of the anniversary on Thursday of the attack on the magazine.