Through reviews relevant researches, it analyzes the effects of external knowledge acquisition from different knowledge sources (customer, supplier and competitor) on innovation performance of firm, builds the model of knowledge acquisition, absorptive capacity and innovation performance, introduces the absorptive capacity as regulating variable of knowledge acquisition and innovation performance, and puts forward six research hypotheses based on the above relations. It lays a theoretical foundation for the future research about this subject, and also provides new suggestions for the innovation practice of firm which is acquiring external knowledge, cultivating and developing absorptive capacity in order to promote innovation performance.