The invention discloses a method for preparing a ceramic membrane on the surface of a non-woven fabric diaphragm used for a lithium battery. The method comprises the steps that to-be-processed non-woven fabric is cut to be in the required size in a purification chamber and then is installed on an unwinding roller of equipment; Roll-Roll vacuum magnetron sputtering coating equipment is started and adjusted to be in a coating process condition; an ion source is started to bombard a polyester non-woven membrane, and a hydrocarbon polymer macromolecular bond part is opened; when a hydrocarbon polymer molecular bond is opened, an intermediate-frequency sputtering cathode is turned on, a Si target material is sputtered through reaction of the intermediate-frequency sputtering cathode, and a SixNy-ceramic material is formed and embedded into the position where the hydrocarbon polymer molecular bond is located; the ceramic membrane is formed; annealing treatment is conducted in the vacuum state, so that the stress of the ceramic membrane is removed; winding-unwinding continuous sputtering coating is conducted; coating of a whole roll of non-woven fabric diaphragm is completed; vacuum breaking is conducted; an unwinding roller is taken down; sampling and performance inspection are conducted; and the non-woven fabric diaphragm is packed and put in storage. According to the method, the pore size and pore distribution of the non-woven fabric diaphragm are improved, and the heat stability and the mechanical strength of the non-woven fabric diaphragm are improved.