The invention discloses a polishing machine waste water collection tank. Two tank bodies are adopted, and the upper portions of the two tank bodies communicate through an overflow communicating pipe.When the water level in a transparent water level pipe communicating with the first tank body is higher than a high water level optical sensor, if the dirty high water level optical sensor on the inner wall of the transparent water level pipe cannot detect the water level, the waste water level in the first tank body is increased continuously, and waste water enters the second tank body through the overflow communicating pipe; and when the water level in the second tank body is higher than a floating ball sensor, a second water suction pump starts to work and to discharge waste water in the second tank body out. Due to the fact that the mechanical floating ball sensor still can detect the water level with factors such as dirty water, waste in the second tank body can be discharged out in time, the effect that waste water in the first tank body can be discharged out through an overflow port in time is ensured, the situation that waste water overflows from an observation window on a topcover of the first tank body is avoided, and the operation safety of the waste water tank is effectively improved.