Abstract: As a heat exchanger between the primary side sodium and secondary side water, the steam generator (SG) is a crucial equipment ensuring the safe operation of the reactor. Thus it is essential to analyze the hydraulic characteristics in primary side of SG. In this paper, a numerical investigation of three-dimensional thermo-hydraulic characteristics in the primary side of a fast reactor steam generator is simulated based on the porous media model. The momentum source term for the porous media model is obtained by investigating the flow characteristics in tube support plates (TSPs) and tube bundle region. The heat transfer from secondary coolant to primary sodium is calculated by RELAP5 code, and the energy source term is compiled into FLUENT solver by user defined functions (UDF). The thermo-hydraulic characteristics of the SG are obtained by solving the governing equations by ANSYS FLUENT solver. The accuracy of the simulation is verified by comparing with the designed data.