An operation method of a proximity sensor comprises: controlling a light-emitting element by a processing circuit. Such control includes a plurality of light source on and light source off operations. An optical sensor receives light and outputs a sensing signal corresponding to the intensity of the light. The processing circuit computes the sensing signal to produce a sensing result. The plurality of light source on and light source off operations includes a group having two light sources on operations and two light sources off operations. The two light sources on operations in the group or the two light sources off operations in the group are performed consecutively. In this way, the ambient light components of the light source on and off operations may cancel out each other to reduce the ambient light components contained in the sensing results.