Abstract: In the core physics real-time simulation,the traditional Alternative Direction Implicit（ADI） method for solving the neutron diffusion equations requires too much calculation time to meet the real-time demand.In this paper,one fuel assembly is considered as one mesh-cell in radial direction to reduce the calculation time;the adjusting factor is added to the finite difference equations to improve the calculation accuracy.The calculation accuracy and speed are tested by its application to the core physics real-time simulation for Qin Shan NPP PHASE II.The simulation result shows that this approach is applicable for the core physics real-time simulation.With online correction technology,the online real-time simulation is accomplished.