Particle flow drop lubrication is a new green cutting lubrication technology,which can solve problem of medium introduction in traditional particle flow cutting.In order to investigate the influence of particle size on cutting effect,Al2O3 particle flow with different particle size was used to cut 45 steel,and the relationships between cutting force,cutting temperature,finish,tool life and particle size were analyzed to find out reason.The experimental results show that particle size has an influence on cutting effect,and there is an optimal particle size.Too large or too small particle size can lead to deterioration of cutting effect. Too large particle size affects the penetration of particle flow into friction surface,and too small particle size cannot adapt rough and violently changing friction surface.Both of them limit separation and leveling effect of particle flow,resulting in poor antifriction effect.Particle flow drop lubrication adopts reasonable particle size,and cutting effect is even better than pouring lubrication.