The invention discloses a method and system for calculating the stock volume of a storage cabinet based on virtual pulses. A frequency changer drive motor drives a conveying bottom belt to rotate to convey the storage cabinet to store materials. The method comprises the following steps: collecting a frequency parameter of a frequency changer, calculating a total moving length of the conveying bottom belt and a current moving length of the conveying bottom belt according to a formula S = V.t, generating a total number of virtual pulses the same as the total stock volume according to the principle that the total stock volume of the storage cabinet is equal to the actual total number of virtual pulses output by the total moving length of the conveying bottom belt, and calculating the number of the output virtual pulses according to the current moving length of the conveying bottom belt to obtain the current stock volume of the storage cabinet; and according to the method disclosed by the invention, the speed of the bottom belt of the storage cabinet is controlled by the frequency changer drive motor, the conveyed materials are calculated by the virtual pulses, the speed regulation of the bottom belt of the storage cabinet and the calculation of the stock volume of the storage cabinet are achieved flexibly, the equipment cost and the maintenance cost are reduced, and the accuracy is high.