A substantial literature has evolved focusing on the synergies generated by the strategic alliances (SAs). In this dissertation, the author chooses Starwood Hotels & Resorts Worldwide as the focal firm, and analyze the cases of SAs formed by its brands, including St.Regis, Westin, W Hotel and Element from year 2008 to 2010. First of all, this dissertation will discuss the development and the general condition of the hotel industry in the United States of America. And then present Starwood Hotels & Resorts Worldwide by analyzing its position in its brands. Also, this dissertation introduces the partner firms and then infers the reasons of the SAs and the synergies created by them. At last, gives the readers suggestions from those cases. According to the overall analysis, there are 5 kinds synergies generated by SAs are shown as follow. (1) synergies generated by brand alliance (2) synergies generated by CSR (3) synergies generated by social relation network (4) synergies generated by market (5) synergies generated by complementary abilities The managers can employ the 5 categories of synergies constructed by this literature when deciding partners, scopes and types of SAs. The categories and the practical cases presented will provide more directions and aspects for reference.