The calculation of available water supply has a number of preconditions.The water supply under the traditional concept is generally calculated under a certain condition, the change of calculation conditions is insufficiently considered. As a result, there is a big difference between the calculation of water supply and the actual situation, it is difficult to meet the requirements of the application of the dynamic changes.This paper built a dynamic calculation mode to overcome the problems. The mode combined some situations such as different dispatching water, irrigation demand, ecological demand, water diversion flow and so on. Taking Heihe water diversion system as an example,the paper developed the dynamic simulation system of water supply of Heihe water diversion system by using the technology of knowledge map and components. Application results show that the simulation system can carry on dynamic calculation for water supply under the different calculation conditions of Heihe River water diversion system, so as to better meet the water volume calculation and decision-making needs under different application requirements. The dynamic calculation mode and simulation system has good operation, strong adaptability and convenient application.