In order to estimate line-of-sight (LOS) angular rate of strapdown seeker accurately, strapdown optical image seeker mathematical model is established. According to the relative motion between missile and target, LOS angular rate estimation algorithm is researched. The required algorithm coordinates are defined, strapdown seeker and gyro models are also established. According to the relative kinematics and attitude relationship of missile and target, the nonlinear state equations of LOS angular rate are given. Aimed at filtering accuracy and real-time application problems, LOS angular rate estimation algorithm based on unscented Kalman filtering (UKF) is proposed. Hardware in loop simulation system are established, and experiments are carried out. The result shows that, the maximum estimation errors of LOS angle and LOS angular rate are 0.37° and 0.68°/s, the estimation accuracy are 0.1008° and 0.2116°/s, respectively. Algorithm running time is about 3.8 ms in digital signal processor, the estimation algorithm can meet the accuracy and real-time performance requirements of guidance system simultaneously. LOS angular rate estimation algorithm based on UKF provides a theoretical basis for engineering applications of the strapdown optical image seeker.