The invention discloses a preparation method of a low-closed-pore-temperature diaphragm. The preparation method comprises the following steps of 1, mixing polyethylene, paraffin oil, an antioxidant and polyethylene wax in proportion to obtain a mixture, 2, conducting heating to 130-140 DEG C to obtain a melt, 3, preparing the obtained melt into a casting piece, 4, stretching the obtained casting piece, and extracting to form a microporous membrane, and 5, carrying out high-temperature heat setting on the obtained microporous membrane to obtain the low-closed-pore-temperature diaphragm. According to the preparation method, the polyethylene wax is added into the polyethylene, the paraffin oil and the antioxidant, and the characteristic of low melting point of the polyethylene wax is utilized, so that the hole closing temperature of the diaphragm is reduced on the premise of not influencing the basic functions of the diaphragm, and the safety of the lithium ion battery and surrounding parts is better protected.