Abstract: A water-sand inrush disaster in thick, water-rich sandy layers during underground construction often leads to extensive surface subsidence. Current research on the spatial-temporal patterns and processes of surface subsidence caused by water-sand inrush remains inadequate. To fill this gap, this paper designed a large-scale visual model test box for water-sand inrush disasters, using wind-blown sand containing 1%, 5%, and 10% clay particles. Experiments were conducted under different water pressures and clay contents to study the spatial-temporal characteristics of surface subsidence due to water-sand inrush. The results showed that water pressure mainly affected the initial rate of sand inrush but had little effect on the final shape of the subsidence trough. Clay content significantly influenced both the sand inrush rate and the final subsidence form: as clay content increased, the affected area and the total volume of displaced sand decreased, while the time required for subsidence stabilization increased. For sand with clay content < 5%, the subsidence trough exhibited a two-stage characteristic—a sharp drop followed by a slope; for clay content> 10%, the trough showed only a slope without a distinct steep drop section. Based on these results, a quantification function was established to describe the surface subsidence troughs caused by water-sand inrush, and its practicality was verified through a real engineering case. This study provides a reference for estimating the extent and volume of surface subsidence induced by water-sand flow in water-rich sandy layers.