Three militants wearing suicide bomb vests entered the college late on Monday, reportedly taking hostages. A major security operation lasted for hours and all attackers were killed.
So-called Islamic State (IS) said its fighters had carried out the attack, although officials have blamed another militant group, Lashkar-e-Jhangvi.
Quetta, the capital of Balochistan province, has seen similar attacks by both separatists and various Islamist militant factions in recent years.
Hundreds of trainees were evacuated from Balochistan Police College as troops arrived to repel the militants. Local media reported at least three explosions at the scene.