The thixomolding solidification process of an AM60B magnesium alloy heavy truck steering wheel frame was taken as the research object. Given that the bulk of the casting material is difficult to fill in the isolated liquid phase during the solidification process, the mold cooling and overflow system was optimized via ProCAST software, and the optimal production process parameters were determined. To change the local cooling conditions, a local cooling pipe was designed in the mold with the greatest part of the casting thickness, and the solidification process after the mold improvement was simulated and analysed according to the adjustment of process parameters. The optimum process parameters are the injection temperature of the semisolid slurry at 598 ℃, the injection velocity at 2 m/s, and the preheating temperature of the mold at 160 ℃. Under these parameter, the shrinkage defect content is reduced from 2.27 cm3 to 0.23 cm3, which is a reduction of 89.8% and can meet the actual production requirements.