The invention discloses a preparation method of a polyolefin catalyst spherical carrier, which comprises the following steps that: (a) dissolving anhydrous magnesium halide into tetrahydrofuran to form solution; (b) slowly adding glycol ether into the solution and stirring, and the molar ratio of the glycol ether to magnesium chloride is 2.5 to 0.5:1; (c) keeping the solution obtained in step (b)still, separating out a bottom layer, precipitating and washing, and upper solution is recyclable; (d) soaking precipitate obtained in step (c) with chloride or alkyl aluminum solution, separating out the precipitate, and washing the precipitate with alkane; and carrying out all operation without water or oxygen and under the protection of nitrogen. The polyolefin catalyst spherical carrier prepared through the preparation method has larger surface area and higher bulk density, so that a catalyst has higher catalytic efficiency in polymerization reaction.