The mechanism of science and technology supporting water environment governance is systematically analyzed from the aspects of demand, condition and path. The results show that the support demand of science and technology in water environment governance is mainly focused on the demand of basic theory and cognition, key technical methods and system solutions. The prerequisite for the supporting role is the development of ecological science and technology. Moreover, the element of playing the supporting role includes the internal conditions like the scale, knowledge, system and corporate culture of the relevant suppliers, and the external conditions such as market, social culture, science and technology, finance, policies and laws. The science and technology play the supporting role in the water environment governance through improving water security guarantee technology and monitoring technology at the level of hard power, and strengthening the institutional foundation, promoting the governance work, and enhancing the public awareness and education at the level of soft power.