Abstract: An engineering simulator of Pebble-bed Modular High Temperature Gas-cooled Reactor (HTR-PM) was developed by embedding THERMIX code into the vPower simulation platform. In the engineering simulator, the two steam supply systems including two reactors, two primary loops and two steam generators were simulated by two THERMIX/BLAST modules respectively, and the simulation model of entire steam turbine generator system was built by using vPower simulation platform. The vPower platform synchronizes the two THERMIX/BLAST modules in executing simulation of two reactor module-structures of HTR-PM. The engineering simulator can simulate the behavior of HTR-PM under steady state, and also can simulate the transient accident conditions of the reactor system.