Existing researches always omit the input resource diversity in the collaborative new product development investments． This article，by taking both the input of capital and knowledge into consideration，discusses the participants’optimal investment decisions． We build a Stackelberg model and discusses the leader and the follower’s investment decisions when the input only contains capital and when the imputs also contain both capital and knowledge respectively． Then the paper compares the similarities and differences between the partners investment decisions in the two cases． We found that with different resources inputs，cooperations need different conditions，namely，only when the leader’s earnings proportion is greater than the follower’s，is it possible to consider inputting both capital and knowledge; the level of knowledge spillovers，which can stimulate the success of cooperative development，can be improved by changing the amount of capital investment， knowledge inputs and R＆D effort extent．