In this paper, a gas detection system using intra-cavity laser spectroscopy technique is designed. It can be used to measure the concentration of multi-gas. Through analysis of the basic architecture and principle of gas detection system, the different standard concentration of acetylene gas is measured and the performances of gas detection system have been evaluated by calculating the absorbance of standard gas, such as detection sensitivity of the system, repeat accuracy and measurement precision. The experimental results indicated that the repeat accuracy of the gas detection system is less than 0.07. The detection sensitivity and measurement precision is less than 0.03％ and 0.17％, respectively.