Abstract: This paper focuses on small nuclear power plant which adopts OTSG. Based on static mathematical models of some important parts such as reactor core, steam generator etc., combined with the control strategy of MRX, the paper simulates the dynamic feature during load following process of small NPP. Moreover, the paper analysis the operation coordination via heat transfer time and control time delaying. According to the Matlab/Simulink simulation results, the control strategy of MRX is valid and suitable for the power following of NPP. The operating time of the second-circuit system is relatively longer, and the response rate feed water flow is lower than that of the nuclear power changing. In practical application, it should be considered to adopt the fast response electric pump.