Abstract: Based on the Reynolds-averaged Navier-Stokes(RANS) equations and structured grid (surface to surface) technique, the effect of different grid density on simulation results of a part-span trap wing configuration is analyzed with MUSCL scheme and SST turbulent model. The corresponding experiment was accomplished in NASA Ames 12' PWT in 1998, the experimental data included the aerodynamic characters and pressure distribution The presented research work includes the influence of grid density on convergence history, aerodynamic character, pressure distribution and surface streamlines. The variation of aerodynamic characters with the angles of attack is also presented on the medium grid. The numerical results indicate that the grid density has little influence on convergence history, pressure distribution and surface streamlines at the conditions of Ma=0.15,α=16.7°, and the aerodynamic characters vary monotonously with the grid density. Compared with experimental data, the numerical pressure distributions with different grids are quite reasonable at the typical span sections, the numerical aerodynamic characteristics on the medium grid are in good agreement with corrected experimental data before stall.