Abstract: Through theoretical analysis and numerical sianulatian,the behavior of the fluid flaw in a multilayer reservoir with crassflaw was studied when the reservoir was separated into two sections by a,packer and a drawdown as buildup test was run in one section.It is found that hoth the semilog plot for dra,wdawn and the Rarner plot far buildup have two straight lines,which can determine the praductivities of the testing section anal the whole reservoir.for a reservoir with two layers,skin factors can also be determined.The wellbare pressure difference will become steady in the second straight line periad,which can be used to determine the vertical permeability of the shale between the two sections.It is explained that different wellbare pressures anti diffusivities for different layers are two reasons to cause erassflaw.The properties of the crassflow are discussed and the its calculation method is given.