Abstract: The 3D temporal/spatial dynamics of multigroup neutron inside a cylindrical reactor core was simulated with an improved quasi-static method in the high-temperature gas-cooled reactor engineering simulation system (HTR-ESS). Macro cross section area in this model was fitted with polynomial equations. The state of reactor core was related with reactor thermal-hydraulics using the fitting equations. The control rods in the reactor were substituted with an equivalent absorber based on their characteristics in the high-temperature gas-cooled reactor. This substitution avoided the problem grid mismatch due to the movement of the control rods in the computation. The method could solve the kinetics equation in real time. A preliminary simulation by this method shows that the new real-time computation model for the reactor physics satisfies the design requirements.