To study the structural performance of geopolymer concrete, a full-scale static load test of reinforced geopolymer concrete simply supported beams is designed to analyze the damage process and damage pattern of reinforced geopolymer concrete beams. Based on the test, a numerical model is established by numerical simulation using ABAQUS software. The dimensional sensitivity is further analyzed by finite elements based on the test. The experimental results show that the damage of the reinforced geopolymer concrete beam is characterized by ductile damage. The results of the size sensitivity analysis show that a reasonable mesh size division is essential for correctly analyzing the structural response, and the finite element results of the fine mesh show better agreement with the experimental results. The developed finite element model can be used as an effective tool for future design and application, which is of great significance for further research on geopolymer concrete and its application in engineering.