Tunable diode laser absorption spectroscopy (TDLAS) technology is inevitably interfered by optical fringes, detector noise, and circuit noise during measurement, which results in large output fluctuations. The use of the Kalman filter to post-process the measurement results can effectively improve the measurement precision and anti-interference ability of the TDLAS system. This study focuses on the ratio g of the measured noise covariance σV2 to the process excitation noise covariance σW2 in the Kalman filtering algorithm. Starting with the fluctuation and the response time of the Kalman filter output, the comprehensive effect evaluation index R of the filter is obtained by assigning them different weights, and the comprehensive research on the relationship between R and g shows that the optimal g is 27. Moreover, the advantages of Kalman filtering in anti-interference and stability over smooth filtering and extended state filtering are verified by simulations. The Kalman filter with optimized parameters is applied in the TDLAS ammonia escape detection, and the measurement precision of concentration of NH₃ with a volume fraction of 4.7×10^-6, concentration of NH₃ with a volume fraction of 108×10^-6, H₂O concentration, and temperature is increased by 3.54, 3.48, 3.00, and 2.80 times, respectively.