Abstract: In order to solve the problem of ethylene detection of trace concentration in biomedical, petrochemical industry, CO2 laser was used to excite photoacoustic spectroscopy effect in photoacoustic cell for ethylene concentration detection. Parameters of photoacoustic cell was designed and optimized. The relationship between laser lines 10P(16), 10P(18) and ethylene absorption coefficient was investigated, and the link of ethylene concentration and photoacoustic signal was studied. Through theoretical analysis and experimental research, the results show that parameters of photoacoustic system are: center of resonant frequency of 833Hz, quality factor of 20.8, and photoacoustic cell of 2323Pacm/W. When laser power is 3.6W, photoacoustic signal and ethylene volume fraction get good linear relationship under the irradiation of two laser spectrum. Linear fit is 0.99744 and 0.99802 respectively. The minimum detectable concentration of system is 0.9nmol/L. Experimental results and theoretical analysis verify the effect of photoacoustic spectroscopy detection of trace concentrations of ethylene has good appliciation value.