This paper presents an indoor pedestrian positioning system that integrates WiFi propagation model and inertial navigation system (INS) to combine the advantages of two systems. Zero update (ZUPT) is adopted to limit the accumulative errors of INS. The signal strength of WiFi is detected to compare with the threshold, when the signal strength exceeds the threshold, the position information obtained from WiFi propagation model works as an assisted positioning for INS during ZUPT. Extended Kalman Filter (EKF) is employed to compensation positioning, velocity and attitude errors. The positioning results show the position errors can be effectively reduced and the positioning accuracy can be increased by the proposed INS/WiFi propagation model integrated system.