The etching of low energy argon (Ar) ion beam of 0–1000 eV on Be was investigated. Different surface polishing methods were compared. Results show that the high-quality Be surface can be obtained by Ar ion beam etching. With the etching proceeding, the Be surface quality is gradually improved, and the surface roughness becomes stable, reaching 0.63 μm after etching at 600 eV and 100 mA for 6 h. White light interferometer (WLI) and focused ion beam (FIB) measurement methods were compared. Results show that FIB measurement method is more suitable for measurement of Be etching thickness. The experiment results and theoretical calculations suggest that the Be sputtering process is similar to the ionization process of Be by Ar ion bombardment. The influence law of Ar ion energy on sputtering yield of Be can be obtained with the first ionization energy as the sputtering threshold, and the variation of Be etching rate with the product of Ar ion beam energy and sputtering yield is obtained, providing foundation for engineering application of Be etching.