The invention provides a preparing method for electrically transforming competent cells without a buffer solution, and belongs to the technical field of molekulare bakteriengenetik. The preparing method comprises the following steps that colibacillus is inoculated into a liquid culture medium containing magnesium ions for first culture; the first culture is mixed with the liquid culture medium, and then secondary culture is conducted to obtain a second culture, the second culture is subjected to centrifugal separation, and precipitation is obtained; the precipitation is mixed with water, afterthe precipitation is suspended, centrifugal separation is conducted, and precipitation is obtained; the precipitation is mixed with water, after the precipitation is suspended, centrifugal separationis conducted, precipitation is obtained, the operation is repeated one time, and precipitation is obtained; the precipitation is mixed with water, after the precipitation is suspended, centrifugal separation is conducted, and precipitation is obtained; the precipitation is mixed with water, after being suspended, the precipitation is evenly mixed with dimethyl sulfoxide, and electrically-transformed competent cells are obtained. By means of the preparing method, the high- transformation-rate competent cells can be obtained, the operation is simple, and the preparation cost is low.