本文在塑性变形体积不可压缩的条件下导出了以塑性应变εｐ定义的塑性泊松比μｐ和以弹塑性总应变εｅｐ定义的弹塑性泊松比μｅｐ的计算式，指出在小变形范围内可以看作μｐ＝０．５，而μｅｐ则总是小于０．５；当变形较大时，无论是μｐ还是μｅｐ均远小于０．５。本文提供的计算式可用于解决大变形问题 In this paper, the plastic Poisson’s ratio μp defined by plastic strain εp and the formula of elastic-plastic Poisson’s ratio μep defined by elastic-plastic total strain εep are deduced under the condition that the volume of plastic deformation is incompressible. It can be seen in the range of small deformation For μp = 0.5, and μep is always less than 0.5; when the deformation is large, both μp or μep are far less than 0.5. The equations provided in this article can be used to solve large deformation problems