Abstract: In view of the large measurement error of the special pH meter for desulfurization slurry used in thermal power plants, it is analyzed that the purity of lime powder, the flow rate of lime slurry and the deposition of CaSO₃ and CaSO₄ on the electrode surface are the main factors affecting the measurement accuracy of pH value of desulfurization slurry. A special pH value measuring device for desulfurization slurry, which is composed of sample control system, sample separation system, sample testing system, slag discharge system and flushing system, has been developed and put into use in Jinshan Power Plant of Inner Mongolia. The practical application shows that the device can accurately measure the pH value of desulfurization slurry, and it is an effective means to improve the desulfurization efficiency.