As an environment-friendly low energy-consumptional green cleaning method, laser cleaning has important applications in paint removal. The removal of paint from steel substrate with a 1064 nm acoustic optical Q-switched quasi-continuous-wave Nd:YAG laser is reported. The influences of laser peak power density on the cleaning result and substrate damage are investigated by numerical simulations and experiments. And the effect of the overlap ratio of laser spots on the cleaning result is investigated. The results show that, during the process of steel substrate paint stripping, the effective mechanism is vibration effect under the condition of threshold cleaning, and it is the combination of vibration effect and ablation effect under the condition of damage cleaning. For the paint with a thickness of 50 μm on the steel substrate, average power of 20 W and more than 80% overlap ratio of laser spot are effective to remove the paint while keeping the substrate undamaged. With the increase of laser power, repetition rate and the radius of laser spot, the cleaning efficiency increases and the cleaning becomes more effective.