Due to the complex interference between the front and rear rotor of the tandem helicopter, the flow field analysis of the aerodynamic interference between the two rotors is carried out in this paper. Firstly, a numerical research method based on momentum source model and N-S (Navier-Stokes) equation is established. The k-ω SST two-equation turbulence model is selected, and the pressure-based implicit solver is used. The established solution method is verified with examples. Subsequently, the numerical simulation of the front and rear rotor flow fields of the tandem helicopter in the hovering state, the forward inflow state and the backward inflow state is carried out, and combined with the calculation results and the flow field characteristics, the aerodynamics generated by the interference flow field are carried out.The results show that for the example in this paper, the rotor performance is reduced for the front and rear rotor in hover, and the rear rotor has a great influence on the performance of the front rotor. The rear rotor lift loss is greater than that in hover in the case of forward flow, and the rotor lift loss is more obvious in the case of backward flow, and the max loss is nearly 50%.