Developing efficient,stable and economical electrocatalyst for oxygen evolution reaction (OER) is a sig-nificant pathway to produce clean energy from water splitting.Herein,the promising and highly efficient porous CoCrFeNiMo high entropy alloys (HEAs) were prepared by microwave sintering using Mg space holder.Owing to unique properties of high entropy alloys and abundant active surface area,the porous CoCrFeNiMo-20 Mg exhibits excellent catalytic performance and prominent electrochemical stability with a low overpotential of 220 mV to reach current density of 10 mA cm-2,a small Tafel slope of 59.0 mV dec-1 and long-term durability for 24 h in 1.0 M KOH.The results of microstructure and element states indicate that crystal defects,porous structure and villous hydroxides are the reasons for high OER performance of the CoCrFeNiMo.This work not only provides a new way to prepare electrocatalysts,but also proves the important application of high entropy alloys in functional materials.