The paper mainly studies the deformation monitoring of tunnel engineering based on 3D laser scanning. First, the principle and characteristics of 3D laser scanning technology are expounded, which lays a theoretical foundation for the research. Then, the flow and main technologies of tunnel engineering deformation monitoring are analysed. Among them, the general process includes four stages: preliminary preparation, point cloud data capture, point cloud data processing and deformation analysis. The main technologies include point and data pre-processing technology and tunnel axis fitting. Finally, combined with the case, deformation monitoring is implemented to analyse the deformation of the tunnel in detail.