The invention discloses a method for preparing urea-formaldehyde glue, and relates to the technical field of adhesive. The method selects formaldehyde, urea, melamine, sodium hydroxide, formic acid, ammonia water, an emulsifying agent, a buffering agent and deionized water as raw materials for preparing the urea-formaldehyde glue, and comprises the following steps of firstly adding formaldehyde and deionized water into a reaction kettle, performing mixing, then putting sodium hydroxide into the reaction kettle, then performing heating, and adding urea for a first time; decreasing the temperature, then adding urea for a second time and melamine, performing heating again, and then adding urea for a third time and the buffering agent; adding formic acid, decreasing the temperature, and then adding urea for a fourth time and the emulsifying agent, and finally adding the ammonia water to obtain the urea-formaldehyde glue. According to the method, the problems of poor initial adhesiveness and high content of free formaldehyde of existing urea-formaldehyde glue are solved.