The invention relates to a preparation method of a crystallite size distribution controllable silver catalyst for preparing ethylene oxide through ethylene oxidation. The method comprises the following steps: (1) carrying out excessive volume mixing on a carrier and a silver-containing impregnating solution, and carrying out catalyst impregnation; (2) carrying out solid-liquid separation on a mixture obtained by impregnation and drying obtained solid-phase particles; and (3) activating a dried solid phase obtained in the step (2) to prepare the catalyst, wherein in any one step or a plurality of steps in the steps (1) to (3), a competitive absorbent treatment procedure is added, a competitive absorbent is a solution of one or more of organic carboxylic acids and/or inorganic carboxylic acids, and a treatment temperature of competitive absorbent treatment is 20 DEG C to 80 DEG C. According to the catalyst provided by the invention, the crystallite size of silver is in a range of 10nm-100nm, and is regularly distributed in the catalyst from inside to outside and from big to small. The method provided by the invention is simple to operate, low in cost and high in controllability; and the silver catalyst with the optimal crystallite size distribution is easy to prepare, and the requirements on improvement of silver catalyst selectivity, stability and the like are met.