The invention discloses a preparing method for a high-performance magnesium alloy bar. The method comprises the following steps that a magnesium alloy raw blank is ground, subjected to homogenizationtreatment, pretreated and preheated, groove rolling machining is conducted, the roller speed ranges from 0.1 m/s to 0.5 m/s, 6-10 rolling passes are adopted, the area of each pass is reduced by 19.8%-24.6%, and the accumulated reduction amount is 71.9%-88.0%. In the groove rolling process, the rhombic hole pass and the square hole pass are alternately conducted, and square hole rolling is adoptedas final rolling; and after rolling of each pass is finished, rolling of the next pass is immediately conducted after the bar is rotated by 90 degrees. After groove rolling is finished, room-temperature cooling is conducted. According to the preparing method, the toughness of the alloy can be obviously improved, and the anisotropy of the alloy is improved. Meanwhile, the multi-direction deformation effect is improved through the adopted novel hole pattern, large strain can be more effectively guided in, the production efficiency is improved, and the preparing method is suitable for producing the high-performance magnesium alloy material in the industrial short process.