The radar cross section (RCS) changes rapidly with the variation of attitude angle during missile flight. Based on the relationship between the two, this paper proposed a missile target attitude angle inversion method using the particle swarm optimization (PSO) algorithm. The method estimated the target attitude angle by minimizing the mean square error between the observed RCS data and the RCS data derived from attitude angle inversion. Theoretical analysis shows that, under the premise that the target attitude angle does not change abruptly within a short time, the proposed method achieves a more accurate estimation of the target attitude angle. A series of simulation experiments was performed, and the results show that the proposed method can effectively invert the attitude angle sequence of the missile target.