The working mechanism of branch pile under vertical load is studied based on digital image correlation method in model test. Bearing capacity and deformation characteristics of equal-diameter pile and branch pile are obtained during the analysis. The study results show that the bearing capacity of branch pile is higher than that of the equal-diameter pile. The displacement field around equal-diameter pile is divided into the pile side and pile tip deformation regions, destruction pattern of single pile is similar to the Meyerhof's destruction pattern. Soil beneath branch generates a shear sliding surface under the ultimate load, and the soil beneath pile tip shows a pricking destruction pattern.