The invention discloses a feed line capacitor configuration method applied to on-line loop closing trend optimization analysis. The method comprises: first of all, calculating the reactive economic equivalents of points, which may be provided with compensation capacitors, on a feed line; secondly, searching for an optimal compensation point; and finally, compensating an optimum compensation capacity on the optimal compensation point of the reactive economic equivalents. According to the invention, the optimal compensation capacitor value is calculated by use of a bisection three curve approximation method for realizing optimal configuration of a feed line capacitor so that the accuracy of an on-line loop closing trend optimization analysis result is ensured.