For the space-time registration errors of radar and IR sensor,a registration model for space and time biases is given and a registration algorithm for on-line biases estimation is presented.By incorporating sensor misalignments and target states into an augmented dynamic model,the dynamic equation of the augmented state and the augmented measurement equation are constructed.Then through the analysis for nonlinearity of the augmented measurement equation,a method of two stage filtering of Unscented Kalman Filter (UKF) and KF is proposed to estimate target states and register radar and IR sensor simultaneously.Furthermore,by comparison with the method of only using UKF,the proposed method has higher accuracy of estimation and less computation.The simulation results show the availability and practicability of the proposed algorithm.