The invention discloses a method of operation range calculation and judgment after single-vibration-area small hydropower station clustering control, comprising the following steps: S1, calculating the sum of rated capacities of all units; S2, calculating the sum of lower limits of the vibration areas of all the units; S3, calculating the minimum value of upper limits of the vibration areas of all the units; S4, calculating the maximum value of the upper limits of the vibration areas of all the units; S5, getting a vibration area of small hydropower stations after clustering; and S6, getting the operation range of the small hydropower stations after clustering. In the prior art, one operation area is selected for each hydro-generator unit, the interval number of the operation area of the unit and the interval number of the operation areas of other units are added together, and union operation is performed on the calculated operation areas to get the operation range after clustering. Computation is complex and heavy in workload. The technical problem is solved using the method of the invention.