The track beam supported by pile foundation is a continuous beam structure with elastic support. It is found that the larger the track beam size is，the safer the structure is. When the load and foundation parameters are similar，the track beam size and pile foundation layout adopted by different engineers are also quite different. Aiming at this problem，this paper analyzes the internal force of track beam from three aspects，i.e. vertical compressive stiffness of pile foundation，pile distance and stiffness of track beam. The results show that when the load and pile foundation layout are determined，there is an optimal beam height to minimize the amount of reinforcement in the track beam. Further analysis shows that when the load and beam length are certain，the internal force distribution of track beam is only related to the relative stiffness of pile and beam. When designing pile foundation to support track beam，it is necessary to try to calculate the optimal relative stiffness，which can make the internal force distribution more reasonable and save the project cost. Moreover，the optimal relative stiffness interval under different pile distances is given，which can provide reference for the design of similar projects.