The utility model relates to a constant temperature protective device of an electrochemical sensor. The constant temperature protective device comprises a housing, a gas inlet pipe and an exhaust pipe communicating with the housing, and a resistance wire winding outside the housing, wherein the housing is a hollow body composed of a pedestal and a top cover in screw connection, an insulation cover is sleeved over the pedestal, a resistance wire winds outside the outer wall of the pedestal, a gas intake and a gas outlet are arranged in the pedestal, the gas inlet pipe winds outside the resistance wire and then communicates with the gas intake, and the exhaust pipe communicates with the gas outlet, and the outer ports of the gas inlet pipe and the exhaust pipe extend out of the insulation cover. The constant temperature protective device allows electrochemical sensors of a portable apparatus or on-line monitoring device to work under any gas temperature. The constant temperature measuring system of the electrochemical sensor has low requirements on work power, and current signals are converted by a circuit into 4-20mA standard signals for output, thereby allowing direct integration into a gas detection apparatus for data connection. The influence of temperature on the electrochemical sensor is eliminated, and the measuring precision is effectively improved.