With the development of science and technology，VR，AR，MR and other technologies are becoming more and more perfect.As the most advanced technology in virtual reality imaging field，this technology will be widely used in the scene simulation of mountain flood disaster in small watershed.In this paper，the real environment of flood disaster prevention and control is composed of virtual scene by MR system，using professional engine to exchange data with GPU，dynamically rendering analog light source，simulating and demonstrating mountain flood disaster outbreak in MR，and combining with the construction of local flood disaster defense system to simulate demonstration of local monitoring， emergency response， relocation， emergency rescue and disaster relief during the process of disaster occurrence.The technology will make full use of information technology to improve the level of flood control management at the grass-roots level，improve the consciousness of disaster prevention and disaster reduction，and reduce the casualty and property loss caused by mountain torrents．