A finite element (FE) model of preforming process of TA15 Ti-alloy complex components has been established based on DEFORM-3D platform. Combined with the experiments, the preforming process and typical forming defects have been analyzed. An excellent preform with good macroscopical forming quality, uniform and fine microstructure has been fabricated using an optimized billet with the proper initial shape, which is acquired by a systematic stepwise reverse optimization method, effectively avoiding the defects of underfilling and folding in the preforming process. The preforming experiment was carried out based on the optimized initial billet and the result of optimization has been verified which is reasonable and reliable.