Reduction of the iron loss and copper loss of induction motors has been thoroughly studied in a conventional sense. However, the fact that no method for estimating the harmonic loss due to the materials or dimensions of a motor has yet been established, has been an obstacle to harmonic loss reduction. We proposed an evaluation index E_w² for the harmonic loss that is caused by slots of a capacitor motor, which is a kind of a single-phase induction motor. E_w² is calculated from effective value of electromotive force with a virtual coil of the rotor surface. On no load, we found that E_w² was effective as an evaluation index for the harmonic loss. In this paper, we calculate E_w² on load and examine the propriety of using E_w² as a harmonic loss evaluation index.