Abstract: In this paper,the development of a compact engineering simulator of the HTR-PM by em-bedding THERMIX code into the vPower simulation environment is introduced firstly.Then the structure of the simulation system of secondary loop is presented in detail,based on the vPower simulation platform.Steady state and transient conditions of the HTR-PM have been studied by the help of this simulation system.The results show that the errors of the steady-state value and design value are within 2%.At the rated operating conditions,the typical transient response curve of the main valve down-step and feedwater flow reducing have rational trend,and the indicators and the final stable value of the dynamic response meet the requirements.The condenser circulating water disrupts for the closing of the circulating water pump causes low condenser vacuum,and the regulating valve quickly closes,the main steam flow decreases and the turbine trips.