The invention relates to a measuring method for the storage capacity of a reservoir (2), and a measuring system is composed of pressure sensors (3, 8), a laser sensor (4), a sonar sensor (5), an adopting camera (6) and a pc (personal computer) machine (7). The measuring method comprises the steps of utilizing the laser sensor (4) to measure the upper surface area of the reservoir (2), and meanwhile starting the camera (6) to take pictures; utilizing the sonar sensor (5) to measure the depth of water, and comparing the water depth of a target rod with the depth of the water; correcting the measured data according to reservoir establishing data to obtain surface area, water depth and floor space, thereby obtaining the volume of water; and utilizing the pressure sensors (3, 8) to measure the pressure of the reservoir (2) to a reservoir bottom and a reservoir side. The measuring method provided by the invention automatically measures volume, depth and pressure, the manual operation error is reduced, a dynamic variation condition of the storage capacity is reflected, and more real-time data is provided for a reservoir detection system; and meanwhile, the detection operation is simple, convenient and exact, and manpower, financial resources and material resources are saved.