Based on the difference in spatial coherence between target echo and multi-scattering clutter in underwater lidar system, a spiral phase plate and an additional ring mask plate were proposed to form a spatial filter to separate the target reflected signal from the multi-scattered clutters. Due to the good spatial coherence of the target reflected signal, vortex light will be formed after the target reflected signal passing through the spiral phase plate, while the spatial coherence of scattering clutter will be destroyed by multiple scattering and presented a Gaussian-like distribution according to the scattering law. The use of ring-shape mask plate only allows vortex light to pass through and reach the detector, thereby reducing the effect of scattering on ranging. The above-mentioned spatial filtering device is applied to radar-lidar and pulse ranging underwater lidar systems, which can greatly improve the ranging accuracy of targets in turbid water.