Abstract: A real-time thermal hydraulic model of the reactor core was described and integrated into the simulation system for the high temperature gas-cooled pebble bed reactor nuclear power plant,which was developed in the vPower platform,a new simulation environment for nuclear and fossil power plants.In the thermal hydraulic model,the helium flow paths were established by the flow network tools in order to obtain the flow rates and pressure distributions.Meanwhile,the heat structures,representing all the solid heat transfer elements in the pebble bed,graphite reflectors and carbon bricks,were connected by the heat transfer network in order to solve the temperature distributions in the reactor core.The flow network and heat transfer network were coupled and calculated in real time.Two steady states(100% and 50% full power) and two transients(inlet temperature step and flow step) were tested that the quantitative comparisons of the steady results with design data and qualitative analysis of the transients showed the good applicability of the present thermal hydraulic model.