The T-shaped tube is a common component in aviation pipeline systems and has broad application prospects. However, the severe wall thickness thinning has been the bottleneck problem restricting the application of T-shaped tubes. In order to avoid rupture due to excessive thinning and improve the forming quality, a new rubber compound-forming method combined with the flanging and bulging of the T-shaped tube using a prefabricated hole is proposed. The optimization model of the prefabricated hole is established based on the geometric analysis method and the incremental finite element method. The optimal prefabricated hole is achieved through two iteration optimizations. The experiments for the compound-forming method are carried out to reveal the forming height and the wall thickness distribution mechanism. Both the simulation and experiment results are in good agreement, and the experimental results with the optimal prefabricated are that the maximum thickening rate is 38% and the maximum thinning rate is 14.67% which are satisfied with the requirements of practical production. Compared with the traditional rubber compound bulging forming with the same process parameters, the rupture occurs before the axial feed reaches the ideal feed. The new compound forming method using the prefabricated hole could effectively avoid fracture on the branch’s top. The comparison results are further verified to be the correctness of the prefabricated hole optimization model and the effectiveness of the new compound forming method.