The invention discloses a system and a method for measuring greenhouse gas. According to the system provided in the invention, a spectrometer is placed in an enclosed cabinet which is filled with high purity nitrogen; gas to enter into a sample cell is dried by a Nafion pipe and anhydrous magnesium perchlorate and then enters into a multiple reflection sample cell which is connected with a suction pump, and a computer controls the suction pump to extract gas in atmosphere; a Fourier transform infrared spectrometer is utilized to measure infrared spectrum of a variety of gas, and the computer carries out quantitative analysis on measured gas. The method provided in the invention enables measuring precision of normal greenhouse gas, i.e., carbon dioxide, nitrous oxide and methane, and indirect greenhouse gas carbon monoxide to be improved.