Abstract: The paper analyses why the cutting unit’s hydraulic cylinders of some imported shearer frequently fail to run properly from the design point of view. The causes, which will lead to oil-leakage, etc., conclude the cylinder gland’s sealing O-ring is easy to be damaged during the action of its assembling, the width of the cylinder gland is relatively small and the bending stability of the piston rod exceeds its critical value. The paper puts forward corresponding improvement projects. The similar faults don’t occur to new-made hydraulic cylinders any more utilized the improvement projects. The improvement projects help to solve practical difficulties of the coal mine and provide basic research materials for the high-end development of imported shearers.