Operation of cascade reservoirs has become a main factor in human activities. In order to quantitatively evaluate the change of hydrological situation in downstream rivers caused by the operation of reservoirs (groups), based on the traditional RVA method, a modified evaluation method of hydrological change was proposed. The Yichang-Datong reach of the Yangtze River, which was greatly affected by cascade reservoirs, was taken as a typical research area, and hydrological situation at each station before and after the operation of reservoirs was analyzed. The results showed that the overall change degree of hydrological situation at Yichang Station increased by 8%, which was a high change degree, and that of Datong Station decreased by 12%, which was a low change degree, comparing with the traditional RVA method. The change occurred at the Yichang-Datong station was accorded with the law of gradually weaken influences by the reservoirs. The influence of reservoirs (groups) was mainly manifested in the accumulation of abundant water and the replenishment of dry water. Comparing with the traditional RVA method, values of 18 indexes produced by the modified hydrological change degree method was larger, which could better reflect the influence of cascade reservoir operation on the downstream hydrological situation. This study could provide technical supports for the follow-up study on the hydrological situation analysis of the basin affected by reservoir operation and the ecological operation of the basin reservoirs.