The invention discloses an application of amorphous selenium, and in particular, relates to the application of the amorphous selenium as an optical second harmonic material. Amorphous selenium particles with different particle sizes are prepared by using femtosecond laser liquid ablation of a selenium solid target material, single amorphous selenium particle with the particle size of more than 300 nm has the function of generating near infrared optical second harmonic waves, and an amorphous selenium particle dimer with the diameter of about 200 nm also has the optical second harmonic wave function. The amorphous selenium is presented to have the wide-spectral optical second harmonic wave function for the first time, and the field that traditional optical second harmonic materials are all crystals is broken. The preparation process is simple, the repeatability is good, the stability is high and the cost is low. The amorphous selenium is used as a novel optical second harmonic material, and can replace the traditional materials to be applied in biological detection, medical diagnosis, surface detection and other fields.