An online water quality monitoring instrument based on optical fiber spectrometer is designed. The hardware configuration of optical measurement module

sequential injection module and electrical control module is introduced in detail. The instrument with measurement range of 0

1 mg/L is built up and test is carried out according to standards in environmental protection industry. Experimental results show that the online water quality monitoring instrument can achieve linearity of 0. 3 %

repeatability of 1 %

and indication error is less than 3 %

it has advantages of high precision and good stabitlity. Instrument completely meets the requirement of online water quality monitoring instrument of hexavalent chromium.