Spectrophotometric seawater pH measurement system is an urgent need of device due to its quick speed and high precision. Based on spectrophotometric method and flow injection analysis technique, an automated system for pH measurement of seawater was developed by integrating pump and valve flow path, LED light source, flow cell and spectrophotometer. This measurement system effectively avoided bubbles. The indicator of concentration gradient in the seawater sample was used to correct for the pH perturbation caused by the indicator, thus the operation of system was simple and convenient. with this system, only 1. 5 min was needed for a sample measurement with a precision of 0. 0013 pH units and an offset of 0. 0059 pH units. This system could be used for the rapid determination of pH of seawater collected by laboratory or research ship with high precision pH values.