Abstract: To investigate the effect of ultrasonic pre-soaking process on the quality of parboiled japonica rice, japonica rice was used as raw material, and traditional soaking (soaking at 65 ℃ for 4 hours) was set as the control group. Different ultrasonic powers (100, 200, 300, 400, 500 W) and times (10, 15, 20, 25, 30 min) were used to pre-soaking rice, followed by soaking at 65 ℃ for 1 hour, steaming, drying, and milling to prepare parboiled rice. By analyzing the appearance, processing, physicochemical properties, and cooking quality indicators of parboiled rice, combined with principal component analysis, a comprehensive evaluation model is established to screen the optimal soaking process parameters for parboiled rice. The results showed that ultrasonic treatment can significantly shorten the soaking time of japonica rice, and the stronger the ultrasonic treatment, the higher the degree of gelatinization of parboiled rice, the lower the white core rate, but the darker the grain color; The cracks generated in the grains by ultrasound can improve the cooking and texture characteristics of steamed rice, and enhance the palatability of rice; After comprehensive evaluation, it was found that the comprehensive score of parboiled rice was highest when the ultrasound power was 300 W and the time was 20 min. Under these conditions, the polished rice yield of parboiled rice was the highest, at 78.15%, L^* was 69.94, and the white core rate was 4.00%. The optimal steaming time, hardness, viscosity, elasticity, and chewiness of rice were 20.50 min, 2096.48 g, 38.79 g·s, 0.75, and 861.51 g. Therefore, the optimal soaking process for parboiled japonica rice is to use ultrasound power of 300 W for 20 minutes and then soak it at 65 ℃ for 1 hour.