The rights group said that overly harsh Belgian counterterrorism laws and "heavy-handed" police operations in the past year were undermining efforts to prevent further attacks.
Islamic State-linked suicide bombers killed 32 people at Brussels' airport and metro on March 22, while the same cell was responsible for the November 13, 2015 Paris attacks in which 130 people were killed.
"Belgium has worked hard this past year to prevent further attacks, but its law and policy responses have been undermined by their overbroad and sometimes abusive nature," said Letta Tayler, senior terrorism researcher at Human Rights Watch, who wrote the report.
The report highlighted steps including prolonged isolation of terror suspects, suspension of passports and scrutiny of suspects' phone and email logs without a judge's approval.
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The 56-page report "also details abusive police responses during counterterrorism raids and detentions".
There was no immediate response from the Belgian government.
HRW waid it had probed 26 incidents involving police in which suspects or their lawyers alleged that the police used slurs such as "dirty Arab" or "dirty terrorist".
All but one were Muslim and all but two were of North African origin, it said.
' "Disproportionate responses weaken the rule of law, fuel distrust of the authorities in Muslim communities, and divide society when it needs to unite against groups like ISIS," said Tayler.