Abstract: Since current loudness models are unable to predict loudness under round window stimulation， a loudness model for round window stimulation is proposed in this paper. The loudness model consists of a peripheral auditory model and a data processing back-end. The peripheral auditory model that is able to calculate basilar membrane velocities under free-field acoustic stimulation and round window stimulation and the back-end that transforms basilar membrane velocities into loudness are constructed. The reliability of the peripheral auditory model is verified by comparing the model-predicted results with the experimental data on the outer ear transfer function， middle ear transfer function and stapes velocities under acoustic stimulation， round window stimulation transfer function， frequency selectivity and frequency response of the basilar membrane， and basilar membrane displacement. The reliability of the loudness model is verified by comparing the model-predicted results with the experimental data on equal-loudness contours， bandwidth noise loudness， loudness level of tone with frequency masking， and threshold for complex tones. The results indicate that the loudness model accurately calculates basilar membrane velocities under acoustic stimulation and round window stimulation， and is able to predict the loudness of pure tone， complex tones， and bandwidth noise under acoustic stimulation and round window stimulation.