Abstract:  The zero trust network security architecture is committed to ensure the access security of Internet of Things （IoT） terminal devices. However， the heterogeneous nature of devices and the real-time nature of the data received by the network lead to the increase of network attacks and cannot be effectively defended. Therefore， we propose a method that can effectively and actively determine safety. This paper introduces the idea of rate of change in mathematics into trust analysis， and forms three attribute sets based on trust interval and rate of change： discrete interval， change range， and change frequency. By calculating the above attributes of the entity’s trust value， the entity’s trust situation is obtained， and an overall assessment of the terminal entity’s trust situation is made from the three levels of completeness， accuracy and objectivity. Under the premise of reducing encryption and other means， the above method can evaluate the trust state of the IoT terminal from the perspective of the data， and this evaluation method can provide a basis for the judgment of the IoT terminal more objectively and accurately. 

Key words: zero trust； dynamic evaluation； Internet of Things ,