The invention discloses a protective device used for PH meter sensor, which is characterized in that a ball float is provided at a sensor rear part, a filter screen is provided at the out of the glass electrode of a sensor head, a sleeve is provided at the outside of the filter screen, the filter screen is fixed at the glass electrode of the sensor head by the sleeve, the through holes are uniformly provided at the outer periphery of the sleeve, when the protective device used for PH meter sensor measures the PH value of a liquid medium, the PH meter sensor is placed in the liquid medium, due to the ball float, the head of the PH meter sensor can not be damaged, because the filter screen and the sleeve are arranged on the head of the PH meter sensor, the solid particles in the liquid medium can not connected to the glass electrode, thereby the deposition is not generated, after a segment time of usage, only the filter screen need be replaced. The protective device used for PH meter sensor has the advantages of simple structure, and can effectively protect the head of the PH meter sensor, and the measurement and the maintenance are convenient.