Comparisons between two types of COD on-line monitoring technique of SHZ-4 and JHC-Ⅲ_A are made. Both of them are oxidized with potassium dichromate, but are determined by spectrophotometry and potention-metry titration respectively. It is pointed out that the reason why the big error occurs when the type of SHZ-4 is used for COD on-line monitoring. The problems existing in industrial wastewater on-line monitoring has been analyzed. The future of on-line monitoring techniques are prospected. It is also pointed out that ozone oxidation monitor, high temperature catalysis monitor and total organic carbon monitor are cleaning monitoring techniques. They are the development directions of the on-line monitoring of wastewater containing organic pollutant in the future.