In order to detect quickly and accurately the concentration of components of SF6/N2 gas mixture, a method based on microfluidic thermal conductivity sensor under the control of constant temperature is given, taking into account the influence of trace air infiltration on it, and with the principle of trace O2 concentration detection based on electrochemical sensor, the whole scheme of concentration detection of gas mixture used in field assay was designed and verified. The experimental results show that the system has high detection accuracy (±1% of the whole measurement error) within the effective test concentration range of the sensor. The response speed is fast, the repeatability is good and the performance is stable.