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• A method of removing the interference on the boundary of the printing surface using the height difference constraint is proposed. • The point cloud rows containing defects extracted using the extreme difference of height values are used as the object of study in this paper. • Divide the point cloud rows into segments and recombine them according to different boundaries. • The characteristic parameter matrix of defects is constructed and divided into three main types. Defect detection is a crucial part of the additive manufacturing process. Based on 3D laser point cloud, this paper takes the surface of AM process as the research object for defect detection, including surface point cloud pretreatment and internal defect detection. Aiming at a kind of interference existing on the boundary in the process of AM, we use continuous constraint and improved slope method to deal with it, and discuss two cases of continuous surface and non-continuous surface. The small threshold based pass-through filtering algorithm extracts the external points of the defect boundary by using the fluctuation of the height value, and classifies the defect point cloud by classifying, combining and matching the external points. Finally, experimental verification results show that the accuracy of our proposed surface defect detection method can reach 92.3%. This method can effectively extract relatively complete defects. It provides important technical support for surface quality inspection in industrial automation. [ABSTRACT FROM AUTHOR]