In order to quickly and accurately determine ammonia concentration from the mainstream smoke of cigarettes burning, a detection system was designed based on characteristic infrared absorption method. According to the characteristics absorption curve of ammonia in the mid-infrared, the system was aligned with the strongest absorption peak of wavelength position by a 10.4 μm infrared fixed wavelength laser. Infrared light irradiated mainstream smoke of cigarettes, and interference fringes were collected by the infrared detector array. Combining spectrum database and spectrum analysis algorithm, the concentration of ammonia was solved by Bill Lambert law for the mainstream smoke. Standard spectrum data was selected from the group consisting of NIST spectrum database, combined with noise reduction processing for interfering gases in a variety of mainstream smoke. Finally, the ammonia concentration information was real-time displayed. Using UnicornTM fixed wavelength lasers, and static Fourier transform interferometer with standard suction engine, experiments tested five different brands of cigarettes for its ammonia concentration in its mainstream smoke. For ten cigarettes randomly selected from each brand, it was detected by ion chromatography and the system in the experiments. The experimental results show that the ammonia concentration of detection system is basically the same as the standard value, meanwhile the system is faster, stronger with anti-interference ability.