Abstract: Fatigue damage is an important problem affecting the service safety of 316L stainless steel melted by selective laser technology. Based on the classical nonlinear ultrasonic theory, the variation of nonlinear coefficient with fatigue period in ultrasonic testing of 316L stainless steel melted by selective laser technology under fatigue loading was studied in this paper. The experimental results show that the second harmonic amplitude in ultrasonic testing signal increases obviously after fatigue damage in 316L stainless steel melted by selective laser technology is produced, and the ultrasonic nonlinear coefficient increases gradually with the increase of fatigue period. Therefore, it is feasible to detect the fatigue damage in 316L stainless steel melted by selective laser technology by nonlinear ultrasonic testing method.