Abstract: An online identification algorithm of odometer's scale factor in land used strapdown inertial navigation system is put forward. Because of the pinpoint accuracy of strapdown inertial navigation system in the short time after initial alignment and before navigation, the fadeout memory LMS algorithm identifies the odometer's scale factor through the measurement values of accelerometers. Simulation indicates that the algorithm will be valuable in engineering. So the problem of distance error accumulation will be well solved and the position accuracy of the whole land used stapdown inertial navigation system will be well improved.