The research method based on the dichromate method (HJ828 - 2017) for the determination of water samples with high chloride and low chemical oxygen demand (CODCr) using solid mercuric sulfate instead of mercuric sulfate solution for testing was established. The experiment found that when standard samples with high chloride ion concentration were diluted and measured according to the HJ828-2017 standard method, the measurement results gradually increased with the increase of dilution ratio, and the reproducibility of the experiment was poor, with high requirements for the proficiency and operation details of the experimenters. If the standard samples with high chloride were not diluted, but a certain amount of solid mercuric sulfate was added to shield the chloride ions, the measurement results of the standard samples were all within the guaranteed value range, with good accuracy and precision. The experiment proved that using solid mercuric sulfate instead of mercuric sulfate solution, the method is simple to operate, accurate in results, and has high precision.