The invention relates to the technical field of heterogeneous catalytic olefin polymerization, and discloses a polyolefin catalyst, its preparation and its us. A method for preparing the polyolefin catalyst comprises: (i) providing a thermally activated mesoporous material, with the thermal activation treatment being performed at a temperature of 300 to 900° C. for a period of time of 3 to 48 hours; (ii) under an inert atmosphere, (iia) conducting impregnation treatment of the thermally activated mesoporous material with a solution containing a magnesium component and then with a solution containing a titanium component, (iib) conducting impregnation treatment of the thermally activated mesoporous material with a solution containing a titanium component and then with a solution containing a magnesium component, or (iic) conducting co-impregnation treatment of the thermally activated mesoporous material with a solution containing both a titanium component and a magnesium component, to obtain a slurry to be sprayed; and (iii) spray drying the slurry to be sprayed from step (ii), to obtain a solid polyolefin catalyst component. When used in olefin polymerization, the polyolefin catalysts prepared by using the method provided by the invention have high catalytic activities, and polyolefin products having a narrow molecular weight distribution and an excellent melt index can be obtained.