Abstract: Omnidirectional stereo matching (OSM) estimates $360^\circ$ depth by performing stereo matching on multi-view fisheye images. Existing methods assume a unimodal depth distribution, matching each pixel to a single object. However, this assumption constrains the sampling range, causing over-smoothed depth artifacts, especially at object boundaries. To address these limitations, we propose MDP-Omni, a novel OSM network that leverages parameter-free multimodal depth priors. Specifically, we introduce a depth prior-based sampling method, which adjusts the sampling range without additional parameters. Furthermore, we present the azimuth-based multi-view volume fusion module to build a single cost volume. It mitigates false matches caused by occlusions in warped multi-view volumes. Experimental results demonstrate that MDP-Omni significantly improves existing methods, particularly in capturing fine details.