The invention discloses a method for preparing a high-purity semi-insulating silicon carbide crystalloid under the circumstance of compensating elements without deep energy level. The electrical resistivity of the crystalloid is larger than 106 ohm/cm and can reach more than 109 ohm/cm under a proper condition. The electrical resistivity of the crystalloid is controlled by the fast growth speed of the crystalloid, wherein the speed is fast enough to lead the electrical performance of the crystalloid. The requirement of the special growth of the crystalloid is larger than 0.6mm/h, preferably, is more than 2mm/h, and the crystalloid is crystallized and grown under the extreme nonequilibrium state of thermodynamics to increase the concentration of primary point defects such as a hollow bit, a hollow bit group or an inverse bit, and the like, in the crystalloid; the completely grown silicon carbide crystalloid is fast cooled to be 1000-1500 DEG C with faster temperature-reducing speed to ensure the concentration of the point defects of the crystalloid to be thick enough to compensate the different concentration between the shallow donor and the shallow acceptor which are undesignedly doped to achieve the semi-insulating electric performance. The method improves the electrical resistivity of the crystalloid and reduces the quantity of crystalloid microtubules.