In order to estimate the semi-strapdown seeker line of sight(LOS) angular rate accurately, the Kalman observer using for estimating frame angular rate was researched. Firstly, according to the principle of semi-strapdown seeker tracking, mathematical model of Kalman observer for the state feedback was established. Secondly, based on the characteristics of the encoder error, the optimal estimation theory was used to calculate and analyze the relationship among the estimation precision and the observer parameters. Furthermore, under the premise that guarantees the bandwidth of stabilized platform, the Kalman observers under two different sampling rates were designed. Finally, the digital simulation experiment was done, and the result shows that angular rate estimation precision is 0.098 9 (°)/s with 2 000 Hz sampling rate, better than 0.301 3 (°)/s which sampling rate is 200 Hz. Seeker bandwidth which under two kinds of sample rates is 59.6 rad/s, and the seeker disturbance rejection rate is 1.5%. Improve the seeker stabilization system sampling rate and matching with the corresponding control parameters, can effectively improve the reporting rate estimation precision.