Abstract: The successful application of chromous solution in chemical analysis is still limited. Here we studied how to use it as a reducing agent for reducing mercury with continous liquid flow analysis system and without the disadvantage of forming metastannic precipitation. Hence it can be used for determining and continous monitoring of mercury in environmental waters. The linear relationship between the absorbance and the concentration of total mercury is covered 0.5-6.0 ppb.The detection limit is about 0.1 ppb. The amounts of reagents required and the waste solution expelled each day are small.