Abstract: Alliance portfolio is so significant for firms in the catch-up stage in China. However, existing research on alliance portfolio follows the paradigm of structuralism of social network and pays more attention to the relationship of network structure and performance, lacking analysis of the formation mechanism of alliance portfolio. From the new paradigm of "post-structuralism", this paper build a model of "performance aspiration——partner selection——network structure" to understand the formation mechanism of alliance portfolio. Based on the 506 firms in Zhejiang Province during a period of ten years, the study finds that the social performance aspiration and historical performance aspiration play important role in the formation of alliance portfolio through shaping the characteristics of structure, relation and partner. The theoretical contribution is that, based on “post-structuralism”, the paper focuses on the network heterogeneity to open the black box of the formation of alliance portfolios. The conclusion of the study is meaningful for the construction of alliance portfolio of firms.