Abstract: The secondary circuit fluid network for MHTGR nuclear system was modeled nonlinearly, the pipeline dynamic and network topology characteristics were studied, a differential-algebraic model was established, and a control scheme of modules’ mass flow rate and turbine’s main steam pressure was designed. In the MATLAB/Simulink environment, the model was encapsulated by standards and the secondary circuit fluid network was simulated by the sample of HTR-PM. The result shows that the model can effectively reflect the nonlinear characteristics of the secondary circuit fluid network, and controllers designed make the values of modules’ mass flow rate and turbine’s main steam pressure effectively converge to the reference, and all the control indexes are higher than the control requirements. The simulation platform designed can provide simulation tests, e.g. the selection of integral time coefficient in practical engineering, control of the secondary circuit fluid network of MHTGR with more modules.