The defects of the software and hardware in unmanned aerial system and external malicious attack pose a great threat to the security and safety of UAS.Due to the complex running environment of UAS,many factors are difficult to predict accurately in the development process.Therefore,it is of great significance to adopt an effective runtime security and safety guarantee mechanism.This paper proposes a UAS security and safety threat detection method based on runtime verification.Firstly,after analyzing a variety of security and safety threats that UAS may encounter,the paper defines the threats in discrete-time MTL and presents the corresponding UAS-DL language to describe the security and safety monitoring specification.Then an automatic generation algorithm of security and safety threat monitor is introduced based on the alternating automaton,and security and safety monitoring of multi-UAS is implemented by parameterization method.In order to improve the accuracy of the detection,the method of combining runtime verification with Bayesian network inference is also studied.The experiment is carried out with the actual UAS development simulation platform Ardupilot,and monitors are deployed on the field-programmable gate array (FPGA) hardware independently to avoid excessive usage of UAS computing resources.Experimental results show that the proposed method can effectively detect the security and safety threats of UAS.