Abstract: Aiming at solving the disturbance rejection rate problem produced by scale error of optical strapdown seeker, a real time compensation method for scale error based on Unscented Kalman Filter(UKF) was proposed. The mechanism of disturbance rejection rate caused by scale error was analyzed, and the nonlinear filter model considering scale error was built by missile-target relative motion equation and optical strapdown seeker measurement equation, the UKF algorithm was adopted to estimate scale factors, and the scale errors were compensated by the method proposed, finally a math simulation and a hardware-in-loop simulation were put forward. The simulation results indicate that the scale factors can be estimated effectively by the method, and both of missile system stability and guidance accuracy are improved after the compensation.