The invention discloses a colorimetric detector of an SF6 gas decomposition product. The colorimetric detector comprises a gas pressure stabilization unit, a flow controller, a gas circuit selection valve, a reference gas circuit channel, a colorimetric tube channel, a flowmeter, a display device and a system control unit, wherein the system control unit is connected with the flow controller, thegas circuit selection valve, the flowmeter and the display device respectively; the gas pressure stabilization unit, the flow controller and the gas circuit selection valve are connected with one another in sequence; the reference gas circuit channel and the colorimetric tube channel are both connected to the gas circuit selection valve, and the flow direction of a gas circuit is controlled by thegas circuit selection valve; the reference gas circuit channel and the colorimetric tube channel both lead to the flowmeter; gas is guided in by using the gas pressure stabilization unit. According to the detector, through automatic control for flow and automatic calculation and control for the volume of the gas, a colorimetric tube detection method is brought to the site in a convenient manner,the problems that sample gas is influenced by outside, the representativeness of the sample gas is not strong, the flow in unsteady, and the gas consumption is not accurate are solved.