A vital problem pointed out is that there is no computation in fuzzy mathematics.Fuzyy set transformation is based on "max-min" algorithm and "if … then" fuzzy logical expert system.In this paper,fuzzy set transformation is realized by membership function.First,membership function is proposed to determne the subject uncertainty under the condition of only one index.Then membership function is used to illusrate this uncertainty.Finally the transformation from index membership to object membership is used to determine uncertainty.By discussing reduntant value.It is show that membership transformation is nonlinear.Thus nonlinear algorithm is given.