[Purposes] This paper aims to study the dynamic response and deformation characteristics of pile foundations on slopes under earthquake action, so as to provide a reference for the design and construction of pile foundations for bridges in mountainous areas. [Methods] The particle flow simulation software was used to establish a pile foundation model on a slope, and the detailed parameters of the model were obtained through parameter calibration. The loading of seismic waves was accomplished with the setting of dynamic boundary conditions, and the forms of the pile foundation and the slope were considered to analyze the dynamic response law of the slope and the force and deformation characteristics of the pile foundation during earthquakes. [Findings] Numerical simulation results show that the vibration deformation damage of the slope site with a group pile foundation is smaller than that of the single pile foundation, and the increase in the slope will make the site deformation damage more serious. Compared with the slope shoulder, the acceleration amplification coefficients of the measuring points at the foot of the slope and inside the slope decrease by 27.7% and 37.9%, respectively, indicating that the acceleration amplification effect at the slope shoulder is more significant. The maximal bending moment of the pile body of each pile foundation occurs near the bedrock face, and the absolute values of the maximal bending moment of the pile body of the two-pile group foundation decrease by 18.4% and 19.8% compared with that of the single-pile foundation at the slopes of 30° and 45°, respectively. The absolute values of the maximal bending moment of the pile body at the slope of 45° increase by 9.7% and 7.9% compared with that at the slope of 30° when the pile foundation is in the form of the single-pile and the two-pile group foundations, respectively. The maximal horizontal displacement of the pile body occurs at the top of the pile, and the maximal bending moment and horizontal displacement of the pile body of the group pile foundation are smaller than those of the single-pile foundation. A larger slope indicates increased bending moment and horizontal displacement of the pile body of the pile foundation. [Conclusions] The forms of pile foundation and slope have a great influence on the dynamic response of pile foundation and the deformation of pile bodies. In pile foundation design, a reasonable selection of pile foundation locations and pile foundation forms can effectively improve the seismic resistance of pile foundations for bridges on slopes.