A large-scale titanium alloy supporting plate, with many bosses on it and many ribbed panels of length and breadth, is a large thin-wall complex plate frame structure. Owing to its large scale, the interior quality cannot be assured by conventional means such as hot isostatic pressing, which can be guaranteed only by analysing and optimizing the casting process. After the structure was analysed, different casting processes were designed. Graphite mould casting was simulated with different pouring processes on the basis of Huazhu CAE software. The forming process of the casting was then analysed and predicted. The simulation results indicate that the distribution of defects in the casting is significantly affected by different pouring processes. On the basis of the CAE simulation results, the casting was poured via the optimized casting process and then inspected via X-ray. The results show that the casting is completely formed without obvious surface defects. Moreover, the X-ray inspection results reveal that the distribution of interior defects in the casting is basically consistent with the casting simulation results.