To solve problems like automatic testing line production fault is not easy to find, the found fault is difficult to solve, and other issues, this study introduces a kind of online fault diagnosis method based on improved Hierarchical Signed Directed Graph (HSDG). This method firstly sets up models and hierarchical clusters, gets automatic testing line’s hierarchical SDG model, then outputs SDG model samples combined with the Dynamic Kernel Partial Least Squares-Support Vector Regression (DKPLS-SVR) model to calculate all nodes symbols. Finally, the paper presents the complete fault diagnosis process based on “offline analysis” and “online diagnosis”. The results show that, this method is robust which can improve the diagnostic speed and resolution, the fault diagnosis results have certain ability of explanation and guiding significance in the production.