For the problem of unequal grouping of parallel compensation capacity in substation, a new optimization method based on curve segmentation and clustering is proposed. Firstly, this paper calculates compensation capacity curve by transformer parameters and load curve and takes the maximal value as the sum of compensation capacity. Then it partitions this curve into several segments and clusters these segmentation results into K clusters, in which the number of cluster is equal to the number of capacitor groups, further modifies the clustering results in order to meet the condition of constraint, and takes the difference between two adjacent cluster results as the capacity of each group. In order to get the steady grouping results, it studies the relationship between segment number and grouping results. After the grouping plan is determined, taking the nine-area figure as control strategy. Finally, simulating with an equivalent practical power grid and load profile, the results show both the availability and rationality of this method that power loss is less than the method of equal capacity when capacitor is divided into 3 groups.