The invention discloses an on-line evaluation method of anchor chain flash butt welding quality based on DTW and MDS. The method comprises: creating a 2L*2L database E1 of size 2L*2L; 2, judging whether the system detects a new signal to be tested or not, if yes, then executing step 3; If no, stopping the welding and ending the system process; 3, collecting signals to be tested; 4, carrying out data preprocessing on that signal to be measured; 5, respectively calculating that dissimilar distance between the signal to be measured and the selected 2L historical data; 6, establishing a dissimilardistance matrix E2 of size 2L*1; 7, combining that matrices E2 and E1 to form a dissimilar distance matrix F with the size of (2L +1) * (2L +1); 8, carrying out dimensionality reduction treatment onthat dissimilar distance matrix F to a matrix G of (2L +1) * P; 9, carrying out clustering analysis on 2L +1 P-dimensional data in that matrix G; 10, judging whether that signal to be tested is clustered into a normal signal class or not, if not, processing the fault signal; If yes, determining the signal to be measured as a normal signal, and processing the normal signal; 11, returning to that step 1 to update the database E1; The invention can quickly and effectively identify the faulty welding product, improve the production efficiency and ensure the welding quality.