Abstract: This study aims to develop an NH3 concentration monitoring system based on tunable diode laser absorption spectroscopy (TDLAS) for real-time and in-situ control the environment of livestock and poultry houses. In an air chamber, an optical path was attached to a butterfly laser with a wavelength of 1512 nm as the light source. NH3 concentration was then detected in livestock poultry houses based on the molecular absorption spectroscopy and wavelength modulation technology. To optimize the performance of TDLAS system, the optimal modulation parameters were determined via tailoring the amplitude and frequency of sawtooth scanning signal and the sinusoidal modulation signal, as well as the phase difference between the input and the reference signals. Moreover, the optimal parameters included the heating temperature in an air chamber, system response time, and the average number of second harmonics. Finally, the concentration calibration experiments were used to verify the performance of TDLAS system. The results showed that the optimal second harmonic shape and amplitude were obtained when the frequency and amplitude of sinusoidal modulation signal were set as 9 kHz and 30 mV, respectively, while the scanning frequency and range of sawtooth scanning signal as 1 Hz and 170-215 mV, respectively, as well the phase difference between the input signal and the reference signal as 50°. The concentration calibration test achieved for the standard gas (N2, NH3). There was a good linear relationship between the different concentrations of NH3 and the amplitude of second harmonic (the correlation coefficient of fitting equation r2= 0.9958). The response time of detection system was about 42 s, from the start of air chamber self-inflation to the time when the target concentration of 99% was reached. In the response test, the results showed that the appropriate increase in the flow rate of gas can effectively improve the detection efficiency of system. According to the temperature test, too high heating temperature has led to ammonia oxidation, whereas too low heating temperature cannot effectively limit ammonia adsorption in the gas chamber. The adsorption of NH3 reached the lowest level, when the heating temperature was set as 403 K in the chamber. According to Allan variance analysis, the TDLAS system reached the detection limit of 0.038 mg/m3 when the integration time was 10 s. The average number was set to 5 times, indicating a high accuracy during the stable period of detection system. Performance tests were performed on the system under the optimal system parameters, indicating a comprehensive linear error of 1.00%, and a quantitative comprehensive repeated error of 0.51%. In four concentration conditions, the accuracy and stability of detection system were close to that of the acousto-optic spectrum detection, and better than that of the electrochemical detection. The findings demonstrated that the developed system can present highly accurate detection and stable performance, and thereby to serve as the needs of long-term continuous monitoring of NH3 concentration in livestock houses.