The utility model relates to a balanced hydraulic cylinder of supporting working roll of steel rolling machine, comprising a cylinder body, a piston and a cylinder rod, a hole used to install a self defense block is arranged at the terminal of the cylinder rod, the self defense block is arranged in the hole. The utility model is characterized in that the surface at the upper end of the self defense block arranged at the terminal of the cylinder rod which supports the working roll bearing support is a planar, the lower end surface of the self defense block is a spherical surface, the lower end surface is connected recumbently with the spherical surface arranged in the mounting hole of the self defense block. The utility model has the advantages that: the self defense block can not produce inclined force status, hardness connection is caused between the cylinder rod and the working roll bearing support, so that the cylinder rod does not swing front-back and side-to-side with the working roll bearing support when steel rolling, the force of the cylinder rod is stable, and the service life of the balanced hydraulic cylinder is prolonged greatly. The formation of pits on the working roll bearing support can be avoided. Simultaneously the spherical surface at the lower end of the self defense block can compensate the swing produced in the rolling of the working roll bearing support, and the force status of the balanced hydraulic cylinder can be improved.