Most of recent researches about knowledge spillover in the cooperative R&D focus on the effects of knowledge spillover on R&D investment efforts, profitability of cooperation, and the impact of social welfare from the macro scope, while few researches analyze risks caused by knowledge spillover systematically from view point of the enterprises in cooperation. The mechanism of knowledge spillover in cooperative R&D and the intellectual property risk resulted from them are expatiated, and then the determinants of the risk are analyzed from three aspects, that is, knowledge characteristic, participator characteristics, and alliance characteristics.