In order to achieve the accuracy of short-time navigation of a Strapdown Inertial Navigation System (SINS),a navigation error mathematic model is established, and the effect of inertial device errors on the navigation accuracy of the system is analyzed. Aiming at the characteristic of short-time navigation,the navigation equation of carrier in a navigation coordinate is simplified with strapdown inertial navigation mechanism,then the attitude error equation of carrier is deduced by installation errors of inertial devices and the equivalent zero-shift of the gyroscope. Combing with the navigation equation,attitude error equation and the errors of inertial devices,the mathematic models of velocity errors and position errors are derived. Based on the error mathematic models, the state-space model and the block diagram of error models are established. Finally,a module of error models is built in Matlab/Simulink and is combined with the strapdown inertial navigation algorithm to calculate navigation data in ground within 150 s. The experimental results show that the relative system error of x-axis of navigation coordinate is less than 20%, and those of y-axis and z-axis are less than 4%, respectively. Furthermore, the influences of change of an accelerometer accuracy on SINS navigation errors are analyzed.