The presented study measured the 2 dimensional pH value at sediment-water interface under the bioturbation of Limnodrilus hoffmeisteri using the planar optode technique. The result showed pH gradient was alleviated, which decreased from 1.6 pH/2.5 mm to 0.6 pH/1 cm. A 1 cm-depth buffer zone for the pH was formed in the vicinity of the sediment-water interface (SWI). The process of digging burrows by Limnodrilus hoffmeisteri had significant effects on the distribution of the pH around the SWI, and the pH in the burrow was 0.6 pH higher than that of the outside.