Abstract: Tree diameter at breast height is a key factor in forest surveys, and its high-precision and efficient measurement is of great significance for forestry resource management, urban tree surveys, land acquisition compensation evaluations, and more. To explore the utility of 3D laser scanning technology in measuring DBH, this study experimentally compared four methods—vertical profile measurement, extracted point cloud circle fitting, 3D point cloud circle fitting, and Real-time Kinematic (RTK) measurement—against manual tape measurement, considering the characteristics of laser point clouds and tree DBH. The results show that the vertical profile measurement had the lowest error, with an average relative error of 1.72 cm and a Root Mean Square Error (RMSE) of 2.11 cm, while the RMSE values for the extracted point cloud circle fitting, 3D point cloud circle fitting, and RTK measurement methods were 6.35 cm, 5.34 cm, and 6.21 cm, respectively. Compared to algorithm-based point cloud extraction methods, the vertical profile measurement method eliminates the need for complex algorithms for automatic point cloud extraction and fine manual classification, effectively avoiding the substantial preprocessing time required by high-precision algorithms and saving significant labor time. Thus, it is suitable for projects requiring conventional accuracy.