This paper presents a fast analytical modeling method for an integrated switched reluctance starter/generator (SRS/G). This method extends the basic theory of the Chi model and utilizes the first five components of Fourier series in expression of current-dependent arctangent function to express the whole flux linkage model of SRS/G, which could be built with only nine data points at five positions. Then the electromagnetic torque is further calculated from the proposed flux linkage model. The accuracy of the model is verified via comparison with measured flux linkage and torque data. Afterward, the details of simulation model for an integrated 6/4 SRS/G system are presented and the dynamic performances at starting-up and power generating states are predicted. Finally, more experimental results such as phase currents, output dc voltages at different operations and torque-speed characteristics for a 6/4 SRS/G based on a DSP drive platform are also presented to verify the accuracy and rapidity of the proposed method.