A modeling method applicable to numerical wind tunnel simulation of a mountainous building comprises steps as follows: Step 1, using CAD (computer aided design) software for drawing a graph and establishing a test building model; Step 2, establishing a mountain model in the CAD graph; Step 3, determining the vertical distance L1 between the test building model and a wind field computational domain entrance as well as the vertical distance L2 between the test building model and a wind field computational domain outlet; Step 4, determining the distance between the wind field side boundary c and the test building model, the distance between the wind field side boundary d and the test building model as well as the distance between the ground and the wind field upper boundary; Step 5, obtaining a mountain side boundary extension line from the CAD graph; Step 6, filling the CAD graph to obtain four flat ground areas; Step 7, establishing a wind field space model; Step 8, importing the mountain model, the test building model, the flat ground models and the wind field space model into fluid analysis software, and setting boundary conditions for analysis. The effect of steps at the boundary on the wind field is reduced, and the accuracy of CFD numerical simulation of the mountainous building is improved.