Phosphorus is the main indicating factor of reservoir eutrophication and has strong affinity to sediment. In order to explore the spatial distribution law of phosphorus in reservoirs, a simulation test on the effect of sedimentation on phosphorus adsorption was carried out under the coupling action of different environmental factors. Besides, the formula for calculating vertical distribution of phosphorus concentration in liquid phase was established based on dimensional analysis and multiple regression method. The results show that the vertical distribution of liquid phase phosphorus tends to be thicker at the top and thinner at the bottom of the reservoir due to phosphorus adsorption during sedimentation. The smaller the particle size, the higher the concentration of sediment and the deeper the water depth, the greater the concentration gradient and the more inhomogeneous the vertical distribution of phosphorus in liquid phase. The vertical distribution formula of liquid phase phosphorus shows that the gradient of liquid phase phosphorus concentration is proportional to 1/4 power of sediment concentration, -2/3 power of sediment particle size and 1/3 power of water depth, and the minimum value of liquid phase phosphorus concentration is proportional to -1/20 power of sediment concentration, 1/10 power of sediment particle size and -1/10 power of water depth. The calculated results are in good agreement with those of the simulation test, indicating that the derived formula is applicable to the study of phosphorus distribution in reservoirs.