Water is one of the most critical factors of maintaining and improving ecology environment, retaining ecological balance, at the same time it is also the important supporter for energy flow and substance flow in city ecology system. The reasonable measurement of substance quantity and value quantity of city in restraining water source is also the important basis of green GDP calculation; it is also the important basis to realize ecology civilization and sustainable development of city. Currently, there are fewer research of calculation methods for substance quantity and value quantity for restraining water source of urban greenbelt, it has not formed assessment calculation method with popular meaning, comparatively uniform, suitable for water conservation suitable for urban greenbelt, this article will develop discussion and propose the corresponding suggestion and calculation method, provide lesson and reference to scenically and reasonably carry out the effective calculation and management optimization of water conservation in urban greenbelt.