Abstract: Abstract: Using the typical engine nacelle as the research object, the aerodynamic intlet drag forces are analyzed, and the corresponding numerical method for computing the spillage drag is introduced thoroughly in this paper. By presenting the numerical boundary conditions for nacelle inlet and exhaust where the mass flow, stagnation temperature and pressure have been given respectively, the requirement of the complex internal flow simulation in the engine is avoided, and then the numerical methods of the nacelle flows simulation around the engine and the spillage drag are proposed. By utilizing the NACA-1-81-100 nacelle inlet as a standard numerical test, the availability of the numerical method presented here has been proved. Finally adopting this numerical methods, the flows around the engine nacelle with different inlet mass flow ratios are simulated, and the spillage drags are computed and the relevant reasons are analyzed.