A helicopter landing flow field calculation method based on Navier Stokes equations is established， which can be applied to the calculation of aerodynamic forces on the rotor， fuselage and tail rotor in the landing area. The method uses a cut-body grid for meshing， an implicit coupling solver and a dual-time scheme to simulate the flow field during the landing process. To improve the computational efficiency， the main rotor and tail rotor are modeled as momentum sources in the flow field. The method also employs a polynomial fitting technique to correct the results of the nonlinear flight dynamics model of the helicopter and achieve trim calculations in complex flow fields. The method is applied to the UH-60A helicopter and the SFS2 ship as case studies. First， a single-helicopter trim analysis coupled CFD method is performed to verify its validity. Then， the helicopter safe landing criteria are introduced and used to calculate the theoretical ship helicopter operational limitation for this helicopter/ship combination.