The research on snowmelt process is very important to flood and drought calamity monitoring and forecasting, as well as to water resource management. A distributed snowmelt runoff model based on the "3S" technology has been designed and developed in this paper. The distributed snowmelt runoff model is based on energy balance and water quantity balance, which consists of three parts: grid snowmelt model, grid runoff yield model and grid catchments model. Snowmelt and runoff yield process are all based on grid scale, so the model is provided with distributing character and has strict physical mechanism. An important concept of "Unit Period of Time" was put forward in the paper for time scale conversion, and thereby developed "Degree and Cent Snowmelt Runoff Model", and gave some thoughts for the difficult problem of hydrology time scale conversion. Another important concept of "Freezing and Melting Coefficient" had also been brought forward here, which is aimed to explain the repetitive freezing and melting physical mechanism in the snowmelt period, so it has important significance to exactly hold the snowmelt process. Besides, a Snowmelt Runoff Simulating System had been developed, which adopted methods of the combination of B/S and C/S, using a great deal of remote sensing data, weather data and hydrology data, realizing the arithmetic of the model, as well as the distributed stimulation of the discharge of the typical study area, Juntanghu Basin. Validation of this model with the true measured data resulted an average relative error under 0.18, indicating that the model was able to realize simulating the process of the snowmelt well.