Abstract: In the hot-dip galvanization sector, the four-element alloy, i.e, Zn-Al-Mg-Re and total amount of rare earths in zinc solution can be measured at 675μm wave length with Type 721 Spectrophotometer by employing azo Cl-P Ⅲ spectrophotometry.This method is simple, accurate and applicable for quick analysis in commercial production.