Abstract: Intelligent total station is the general approach for deformation monitoring of the subway tunnel in current use,but the data size is limited and the labor cost is high during information extracting.A method for vertical section Abstraction based on 3D point cloud is proposed in this paper,which can be applied for deformation monitoring.This approach includes 3 parts:point cloud registration,tunnel central axis calculation and vertical section Abstraction.The central axis of a subway tunnel can be determined through RANSAC algorithm and least square adjustment;the orientation of tunnel firstly has to be adjusted in terms of the central axis,then the data can be fitted by local quadric fitting,which includes constrained least squares algorithm and RANSAC algorithm.The feasibility and accuracy of the proposed method have been verified using the point clouds acquired by RIEGL VZ-400 laser scanner,and the practical significance for applications of 3D laser scanning is reflected to some extent.