Abstract: In this study, the in-pile thermo-mechanical constitutive relation of fuel pellet and cladding was introduced into the numerical simulation based on ABAQUS, and the method of numerical simulation of the in-pile behavior of the UMo-Zr monolithic fuel plate was preliminarily established. Based on the method of numerical simulation, the effect of fuel pellet structure on the temperature field and stress field was analyzed by changing the length, the width, and the thickness of the fuel pellet and the shape of the edges. The research results indicated that the temperature field and stress field in the post-irradiation fuel pellet were sensitive to the thickness of the fuel pellet; the peak Mises stress in the post-irradiation fuel pellet was decreased by chamfering the fuel pellet.