The invention discloses a method and a system for measuring and calculating hydroenergy utilization improvement rate of cascaded hydropower stations. The method comprises the following steps that: 1) a data acquisition device acquires actual operating data of the hydropower stations; 2) the data acquisition device transmits the acquired data to a measuring and calculating server; and 3) the measuring and calculating server processes the acquired data, calculates actual generated power and assessed power aiming at the hydropower stations in different adjusting types, and obtains the hydroenergy utilization improvement rate. Due to the method and the system for measuring and calculating the hydroenergy utilization improvement rate of the cascaded hydropower stations, the accuracy of the calculation result of the hydroenergy utilization improvement rate can be improved and a good guiding effect is taken for the scheduling optimization of the hydropower stations.