The utility model discloses an online monitoring device of a sulphur removal process of a thickened oil thermal recovery steam injection boiler. The online monitoring device of the sulphur removal process of the thickened oil thermal recovery steam injection boiler comprises a pH value online monitoring probe (1), a pH value display alarm apparatus (2), a PLC (3) and an electromagnetic valve (4), wherein the pH value online monitoring probe (1) of the online monitoring device of the sulphur removal process of the thickened oil thermal recovery steam injection boiler is installed in a spraying alkali liquor pool (12), the pH value online monitoring probe (1) is connected with the pH value display alarm apparatus (2) through a signal wire, the PLC (3) is installed in a power distribution cabinet (9), and the PLC (3) is connected with electric control elements of the pH value display alarm apparatus (2), the electromagnetic valve (4), a spraying pump (6), a stirred kettle (7) and a dosing pump (8) through leads. The online monitoring device of the sulphur removal process of the thickened oil thermal recovery steam injection boiler is novel in structure, reasonable in design, safe, reliable and capable of timely and accurately monitoring the pH value, ensures good operation of a sulphur removal device, saves times and labor, achieves automatic operations, reduces atmospheric pollution, protects environment, and prolongs the service life of the sulphur removal device.