The invention discloses a special pH measurement device for an electric generator inner cooling water system and a working method thereof. The device comprises a flowmeter, a conductivity flow cell, ahydrogen conductivity flow cell, a degassed hydrogen conductivity flow cell, a flow regulation valve, a multi-channel conductivity table, a PLC control panel, a color-changing cation exchange column,a carbon dioxide remover and an electric regeneration cation exchanger, wherein the flow regulation valve and the flowmeter are mounted on a sampling pipeline which is led out from a water outlet pipeline of the electric generator inner cooling water cooler, moreover, the flow regulation valve and the flowmeter, the conductivity flow cell, the electric regeneration cation exchanger, the color-changing cation exchange column, the hydrogen conductivity flow cell, the carbon dioxide remover and the degassed hydrogen conductivity flow cell are connected orderly according to a water flowing direction; the conductivity flow cell, the hydrogen conductivity flow cell and the degassed hydrogen conductivity flow cell are respectively connected with the multi-channel conductivity table, and the multi-channel conductivity table is connected with the PLC control panel. The device and the method provided by the invention have wide range of application, and can be used for both a stator cooling water system and a double-water inner cooling system.