Abstract: The scale of firm-level R&D is rapidly increasing in China, yet the structure of R&D investment has shown the tendency of imbalance, which may hinder the progress of Chinese economy. This article is based on data from 2004-2014 large and medium-sized industrial enterprises in China, examining the influence of firm size and technology acquisition pattern on the R&D structure (the ratio of basic and applied research to total R&D expenditures). We illustrate that as the size of the firm increases, its R&D structure follows a reverse "U" shaped curve, by which the ratio goes up and falls down after the firm size is beyond one particular turning point; technology acquisition pattern modifies the influence of firm size on R&D structure. Using dynamic GMM, we test the theory and the result also shows that inner R&D and technology purchasing positively modify the relationship between firm size and R&D structure, whereas technology import negatively modifies it. The test also finds that government support, degree of marketing and export play a positive role for R&D structure