To simulate numerically airwake around ski jump decks, the LHA (landing helicopter as- sault) ship was calculated by FLUENT. The accuracy of numerical simulation was verified by the ex- perimental data in wind tunnel. Three different grids were generated to analyze the influence of the prismatic layer grid. The results show that, the presence of prismatic layer grid does not affect the re- sults. Grid refinement along the edges of the ship deck shape is critical to capture the generation of bow and edge vortices. With calculating the full-size aircraft carrier ship, the complex evolution of vortices in the ship deck airwake field is found. For separating vortex from superstructure, the accu- racy of calculation affects the overall characteristics of the downstream flow field. The overall size of the deck shape and the location of the superstructure affect the intensity and the location of the vorti- ces behind the deck.