Abstract: Selecting commercial CD40 lubricant as based oil,a simulation experiment was carried out to study the effect of nano-Al2O3 on wear and friction of cylinder liner/piston ring of diesel engine under various loads.The weight loss and friction coefficient were measured,the morphology and size of wear debris in oil were analyzed using ferrography.In addition,the surface micro-image of cylinder liner samples were investigated by AFM,and the elements of worn surface were analyzed by LAS-3000 surface analysis system.The wear resistance and friction reduction became more capable as the load was higher,which suggested that higher load was favourable for tribo-chemical reaction between nano-Al2O3 and rubbing pair surfaces.