Abstract: A psychoacoustic experiment is conducted to address the effect of visual stimulus on auditory sound source localization in the median plane. The experimental results are analyzed based on perceptual fusion rate (the proportion of perceptual unification of visual and auditory stimuli) and cross-modal localization bias (the degree to which auditory sound source localization is affected by visual stimulus). The results indicate that altering the relative locations of visual and auditory stimuli leads to significant variation in perceptual fusion rate. The effect of perceptual fusion on auditory sound source localization is significant. In the fusion cases, sound source localization is distributed near visual stimulus. In the non-fusion cases, sound source localization is unaffected by visual stimulus and even away from it.