In recent years, near-infrared laser absorption spectroscopy detection technique has developed rapidly, and spectral analysis of absorption lines is one of the important research contents of spectrum detection. The experimental platform for gas laser absorption spectroscopy measurement was established in this study, moreover the experiment of ammonia characteristic spectroscopy analysis at 6528.8 cm-1 and algorithm research were carried out. Experimental results show that the root mean square error of the measured signal reduced 4.45 times after combined with wavelet denoising method, and the fitting residual error of overlapped absorption lines was lower than 2% by using multi-line Voigt line profile fitting algorithm. In the experiment, the ammonia characteristic absorption spectrum of different pressures at room temperature was obtained, and the line strength parameters of each absorption line were also calculated. The relative deviation between the measured results and Hitran database was between 5.67~8.2%，and the uncertainty of calculated line strength was about 4.6%. The accurate measurement of line strength by the effective spectrum analysis algorithm of overlapped absorption lines is in favor for improving the accuracy of ammonia concentration inversion.