Abstract: The uniformity of zinc coat of the hot-dip galvanized steel tube is mainly determined by means of copper sulphade-dip test, and the test result is related to such elements as the purity and pre-treatment of the copper sulphade and concentration, temperature, PH value of the copper sulphade solution as well as volumes of the vessels used for the test. Based on a comparision between test with industrially pure copper sulphade and test with chemically pure copper sul-phade, it was found that dip number of the former is less than that of the latter. PH test of the copper sulphade was also conducted, which shew that the smaller the PH value was, the fewer tests the specimen underwent, and that the optimum PH value was 3. 5.