The invention discloses a roller of magnesium alloy cross rolling and a rolling method of the roller, and belongs to the technical field of rolled magnesium alloy sheets. The roller is characterized in that, the shape and structure of upper and lower working rollers are the same, one end of a roller body is in an s shape, and the other end of the roller body is flat. The rolling method comprises the following steps that (1), a magnesium alloy sheet blank is input to a rolling machine in the length direction to conduct rolling, the reduction rate in first two times is less than 10%, the reduction rate of the third time is less than 20%, and the length of the rolled piece reaches the finished product requirements; (2), in the fourth time, the magnesium sheet is rotated by 90 degrees to conduct transverse rolling; (3), in the fifth time, the upper working roller is moved rightwards, the lower working roller is move leftwards, and cross-roller rolling is conducted, and the reduction rate is less than 15%; and (4), in the sixth and seventh times, the upper working roller is continuously moved rightwards, and the lower working roller is continuously moved leftwards, rolling is conductedwith the flat section of the working rollers, wherein the reduction rate is the sixth time is less than 10%, and the reduction rate in the seventh time is less than 1%, and final rolling is achieved.The rolling method has the advantage that (1), edge crack of a rolled piece is overcome, and the yield rate is improved, and (2), the grain size of rolled product is refined, and the mechanical property is improved.