The increase of corporate R&D input is very helpful for strengthening the corporate ability of self-innovation.In order to analyze the environmental effects of market need,industrial competition and external financial environment on R&D input of enterprises,the panel data of Chinese large and medium-sized enterprises are used.The result shows that the need of new product has a positive impact on R&D input of enterprises,but it is not strong enough;while the intensive competition in industries hasn't shown a general positive impact and the external financial environment needs further improvement.