Using the method of “pessure⁃consumption” and Micro⁃flow measurement instrument the start⁃up pressure gradient of water flooding and microemulsion flooding in low permeability reservoir is actually measured.Analyzed the characteristics of nonlinear seepage and the effect with mechanization of start⁃up pressure gradient of microemulsion in low permeability reservoir.The result show that the pessure⁃consumption curve of low permeability reservoir is a concave⁃up curve which has non⁃Darcy seepage flow characteristic. The start⁃up pressure gradient and permeability in a power,and start⁃up pressure gradient are increasing with the reduction of permeability.The average start⁃up pressure gradient of flooding water is 0.050 MPa/m,and the average start⁃up pressure gradient of micro emulsion flooding is 0.039 MPa/m.The reason why microemulsion can reduce start⁃up pressure gradient is that it can decrease interfacial tension and resistance coefficient.The lower the interfacial tension of micro emulsion,the small start⁃up pressure gradient.