The electrical haulage shearer is an important coal mining machine, and the reliability of cutting unit plays an important role in improving the production efficiency. First of all, the dynamic fault tree of not-cutting failure for the MG550/1220 electrical haulage shearer was established. The dynamic fault tree was analyzed by the binary decision diagram and Markov method in the manner of modular approach. Eventually, the minimum cut sets, the top event unreliability and the importance measures of dynamic fault tree were obtained. Research shows that the improper installation of first shaft bearing, the cage off of the first shaft bearing, the cutting motor damage and the poor quality of lubricating oil are the principal contributor to the not-cutting failure of the shear. Consequently, these parts should be given more attention in the optimization design and routing maintenance.