The invention discloses a preparation process of a lithium battery diaphragm. The preparation process comprises the following steps of: 1, preparing a membrane casting solution; 2, carrying out electrostatic spinning on the membrane casting solution to obtain a prefabricated fiber membrane; 3, performing baking at high temperature; and 4, coating the upper surface and the lower surface of the fiber membrane with a ceramic material. According to the invention, polyimide is modified, a soft chain segment can be introduced into a polyimide molecular chain, the flexibility of the polyimide molecular chain is improved, the flexibility of the fiber membrane is improved, also polyethylene glycol is combined with a membrane matrix in a chemical bonding mode, the binding force is high, the solventresistance and the high temperature resistance of polyethylene glycol are improved, and the diaphragm has efficient and lasting ionic conductivity; besides, the surface of the polyimide fiber membraneis coated with the ceramic material, so that the pore diameter of the diaphragm can be effectively reduced, the average pore diameter of the diaphragm is about 0.1microm, the pore diameter distribution is uniform, and the use performance of the lithium battery diaphragm is improved.