A preparation method of a garment with automatic opening, includes: firstly, a garment opening preform is manufactured, and then an automatic opening garment is prepared by using the preform. In the preform, one or more functional layers with predetermined shapes and sizes are connected to the positioning layer; when the clothing needs to be opened, the preform only needs to be connected with the area to be opened of the clothing, and the incision is made according to the position of the functional layers, so that the positioning is not required by a pair of incisions on the clothing, which is efficient, convenient, concise and easy to adjust, and provides a convenient and accurate template function for the opening of the clothing, namely, opening and using. The functional layer of the garment opening preform is made of hydrophilic material or hydrophobic material.