Various experimental conditions were tested for the green extract process of corrosion inhibitor from lychee fruit waste, and the optimal extract parameters were selected using potentiodynamic polarization. The best inhibition effect of the ethanol extract of lychee's peel and seed by ultrasound for 1.5 h (EELPS) for mild steel in 0.5 M HCl was obtained at 600 mg/L using electrochemical and weight loss measurements. Theoretical calculations illustrate the adsorption sites and adsorption behavior of effective compounds. Due to the existence of hydroxyl groups and phenol rings in the main components, EELPS is considered to be a good inhibitor. (C) 2018 Elsevier Inc. All rights reserved.