Vapor hydrogen peroxide is a strong oxidant. The final product is water and oxygen. It has the advantages of no residue, safety, rapid disinfection and wide material compatibility. Vapor hydrogen peroxide sterilization is widely used in pharmaceutical, medical, health, and biosafety fields to ensure the safety of drugs, medical devices and food, especially used for disinfection and prevention of respiratory infectious diseases such as COVID-19, MERS, SARS and H1N1. In order to ensure the sterilization effect, hydrogen peroxide detector is used to monitor the concentration of hydrogen peroxide. Based on the tunable laser absorption spectroscopy technology of 1 255 cm-1 quantum cascade laser, a vapor hydrogen peroxide concentration measuring device is developed. The concentration range is 0~1 800 ppm. The main parts of the detector are isolated from hydrogen peroxide by V-type optical path structure and optical window to avoid hydrogen peroxide corrosion. In view of the fact that the error of transmittance function approximated by the first-order Taylor series is large in the case of high concentration and high absorbance, the second-order Taylor series is used to approximate transmittance function, and the second-order function of the second harmonic signal with respect to the gas concentration is derived. The second harmonic signal is the voltage value, which is calibrated and traced by potassium permanganate titration. Finally, the measurement formula is obtained, which fits the high and low concentration hydrogen peroxide well, and the maximum fitting error is 3%. When the humidity changes, the second harmonic signal does not change, excluding the influence of moisture on the measurement of hydrogen peroxide, which is suitable for the measurement of high concentration VHP at atmospheric pressure during the sterilization process.