Coal-water slurry flow in pipes was examined by theoretical deduction and numerical calcu- lation,taking the effect of apparent wall slip into consideration.It is shown that the thickness of the slip layer has great effects on flow parameters,even though it's in micron level and the drag reduction resulted from the wall slip depends on the non-dimensional thickness(the ratio of slip layer thickness to pipe radius).The flowrate increases linearly with the increase of the non-dimensional thickness and the slip correction factor grows as the pipe radius increases,and is proportional to the non-dimensional thickness.