Laser photoacoustic spectroscopy is a technique to measure trace gases using infrared laser radiation.This technology is based upon the generation of acoustic wave in a gas excited by a modulated laser beam at a wavelength corresponding to the absorption line of the gas species and at the resonance frequency with acoustic resonator, and on the detection of this sound using a sensitive microphone.This work presents a theoretical and experimental procedure of laser photoacoustic gas detection and measurement of its concentration.The theoretical simulationand the analysis of experimental data have been accomplished using matlab software.Acoustic wave pressure for different gases of industrial and environmental concern like (Freon-12 CCL2F2, Acetylene C2H2, Carbon dioxide CO2,Sulfur hexafluorideSF6 and Ammonia NH3) has been simulated under different conditions. These conditions include changing the laser power range from 3to30mW, resonator diameter (2, 4, 6and 8mm), and the resonatorlength (10, 20, 30, 40, 50and 60mm).The experimental work hasbeen accomplished using Freon-12 gas. This is by fabricating an acoustic resonator of 50mm length and 4mm diameter. A sensitive microphone has been planted in midpoint to detect the acoustic signals.CO2laser of effective power levels 0.7-2W have been used to induce the acoustic wave. Different laser modulation frequencies higher and lower than the calculated resonance value have been forced into the resonator to study the gas reaction according to different concentrations. Time–based measurements of both time domain waves and line spectrum of the fundamental and higher harmonics were recorded to monitor the variation in signal amplitude and their spectrum.The concentration of Freon-12 gas has been measured according to these variations. The gas concentration is interpreted according to line spectrum for acoustic wave of the fundamental and higher harmonics, or sub harmonics at different gas concentrations.