NSHV has complex motion mode and high dynamic characteristics, and the traditional threat assessment methods applied to NSHV are characterized by some deficiencies in the selection of evaluation and the dynamics of evaluation. The flight path of NSHV is divided into three main flight stages. Through analyzing the movement characteristics of each stage and ability of early warning detection and interception, a multistage NSHV threat assessment model is established based on Bayesian inference and decision theory, the evaluation of each stage is correlated with prior probability, ensuring the continuity in the assessment. Finally, a typical scenario is established for simulation verification, the threat changes reflected by the simulation results conform to the operational characteristics and the observed data. The dynamic reflected at every stage shows that the changes of threat at each observation point are more suitable for the dynamic characteristics of NSHV, and for the commanders in making defensive operational support decisions.