It analyzed reasons of the oil leakage of raw mill sealing and cylinder piston head cracking. Under one mill roller, two cylinder piston rod bear different pressure, which caused cylinder fatigued cracking. While replacing hydraulic cylinder，one new simple installing tool was made to adjust the edge between piston rod and clevis end, which insures the same pressure bear by two piston rod of hydraulic cylinder. After replacing hydraulic cylinder, by controlling limestone grain size, the mill output and suitable raw material thicknesses, and strengthening maintenance of mill hydraulic system，hydraulic cylinder cracking problem has been solved completely.