The importance of alliance portfolio management capability in improving performance has been proved, but the progress between them is not clear. Based on the ambidexterity theory, this study divides alliance cooperation into co-exploitation and co-exploration. Then we use the literature review, the questionnaire survey and the structural equation model to explore the impact between the three dimensions of alliance portfolio management capability （proactiveness capability, alliance governance capability, portfolio coordination capability） and firm performance, especially the mediating effect of ambidextrous cooperation. Based on the survey data of 320 companies in the districts of Shanxi, Sichuan and Chongqing, this paper establishes the theoretical model among alliance portfolio management capability, ambidextrous cooperation and focal firm performance. This paper expects to open the black box between alliance portfolio management capability and focal firm performance. The results show that: First, the three dimensions of alliance portfolio management capability exert differential effects on co-exploitation and co-exploration. Second, co-exploitation and co-exploration have a significantly positive effect on firm performance. Third, co-exploitation and co-exploration have a different mediating effect on the relationship between the three dimensions of alliance portfolio management capability and firm performance. The results also show that firms need to pay high attention to the differences in proactiveness capability, alliance governance capability and portfolio coordination capability. Then firms have to flexibly choose co-exploitation or co-exploration in order to obtain a better performance. The conclusions of this study not only expand the antecedent of co-exploitation and co-exploration, but also provide the theoretical support for firms to effectively manage alliance portfolio.