In the investment casting of shifting fork,hot crack is the common defact.in order to analysis the hot cracking in the investment casting,The ProCAST software is adopted, the fork investment casting process is simulated,The filling field,temperature field and stress field is analysised, the cause of crack is predicted. The result shows that: as the local area is received larger tensile stress from around, the shrinkage cavity appears, leading to crack.By reducing the pouring temperature,increasing preheating temperature of the shell, increasing chamfer angle of the fork, the casting stress can be reduced, the crack can be avoided.