Abstract: In order to alleviate the acid inhibition during acidogenesis of solid organic wastes, product-films accumulated around the substrates and microorganisms were hypothesized based on the diffusion of the acidogenic products in this study. Ultrsonic irradiation was introduced to destroy these product-films and promote the acidogenic performance. Direct ultrasonic irradiation could desorb acid from particle surfaces, and hence elevated the VS degradation rate from 0.8 to 1.3%/d. To advance the ultrasonic effect, fermentation broth from previous acidogenesis (volatile acid concentration was 11.0 g/L) was treated by the modified ultrasonic treatment (3-times-dilution-20-min -ultrasonic irradiation-filtration), and then fermented for 10 days in a rotational drum fermentation system. 68.2% of acid was removed from the substrate after treatment. At the end of the fermentation, the volatile acid increasing ratio (RVA) and VS degradation ratio (RVS) were increased from 166.7 and 17.0 to 732.0% and 26.7%, respectively. The results demonstrated that ultrasonic irradiation alleviated the product inhibition and improved the acidogenic performance of solid organic wastes.