To investigate the mechanical behavior of the pile cap for the main pylon of an A-shaped cable-stayed bridge without crossbeams, a realistic bridge of this type was selected as a case study. A grillage finite element model of the entire bridge was established using MIDAS to compare and analyze the effects of three different pile foundation layout schemes on the mechanical response of the pile cap. Subsequently, a local solid model of the pile cap was developed using MIDAS FEA NX to examine its transverse stress distribution under frequent load combinations. The results of comparison and selection revealed that the optimal scheme involves symmetrically arranging "2+2" piles at the dumbbell-shaped necking region in the center of the pile cap. This configuration effectively reduces the span, resulting in a more uniform and reasonable distribution of stress and deformation in the pile cap under frequent load combinations. The load-bearing mechanism of the pile cap is characterized by transverse prestressed steel tendons acting as key "balancing elements". By establishing a prestress field within the pile cap, these tendons directly resist the horizontal thrust generated by the pylon, working together with the passive pile foundation to form a three-dimensional load-bearing system that internally balances, spatially distributes, and transfers the complex spatial forces from the superstructure. In addition, reinforcement meshes should be arranged in the prestress anchorage zones and in the regions between piles at the bottom of the pile cap to resist local tensile stress concentrations and control cracking. Traditional spatial grillage models exhibit limitations in analyzing the mechanical behavior of the thick and large pile caps in such A-shaped pylons, which may lead to distorted results and overestimation of local stresses. Therefore, the use of solid finite element models is recommended for accurate verification and design.