Provided is a preparation method of a catalyst for ethylene (co)polymerization, comprising the following steps: (1) preparing a magnesium compound solution by contact-reacting a halogenated magnesium compound with a mixed solvent of cyclic ether and at least one alcohol; (2) reacting the resulted magnesium compound solution from the above step (1) with a silicon compound having at least one alkoxy group; (3) preparing a support by adding a titanium compound to the resulted product from the step (2); and (4) reacting thus obtained support with a titanium compound and optionally a monoester compound, resulting in a catalyst. Catalysts prepared according to the present invention have a regulated particle shape, and their particle size can be easily adjusted. Therefore, with such catalyst, it is possible to produce polymers having high bulk density at high production yield.