A total of 66 complaints for sexual insults or aggression were lodged between last Thursday, when the carnival got underway and Wednesday morning.
The previous year there were 18 such reports, police said.
However part of the rise could be down to "a change in the attitude of victims and witnesses," the police added.
Local authorities in the western German city had in recent weeks urged any victims to come forward and report crimes to the police.
Women's associations also said that any woman who felt herself being inappropriately touched should make a complaint.
Police in Cologne have been struggling to restore public confidence after hundreds of women said they were groped and robbed in a mob of mostly North African and Arab men in chaotic New Year festivities.
Security fears had been heightened by concern that jihadists might take advantage of the massive influx of refugees into Europe to slip in undetected, with Germany particularly vulnerable after taking in 1.1 million asylum seekers last year alone.
Cologne's police chief has been suspended for failing to stop the mob violence at New Year's Eve celebrations.
With the increased policing for the Carnival events, the incidence of other non-sexual crimes were down compared to last year.