A multi-mode laser absorption spectroscopy system with high detection sensitivity and high stability is built using an F-P multi-mode diode laser near 1570nm as the light source .In order to improve the detection limit of the system,a discrete lens-type multi-pass cell with path length of 100m is employed as the measur ement absorption cell.The multi-mode diode laser correlation spectroscopy,wavelength modulation technology and long-path absorp tion spectroscopy are combined to improve the performance of the system.In the experiment,the laser beam is spitted into two parts,which pass through the reference cell and measurement cell,respectively.The measuring light and the reference light s ignals are detected simultaneously.The performance of the system is validated by measuring the concentration of carbon monoxide (CO).The CO concentrations are derived from the relationship between t he normalized WMS-2f signal peak heights of the measurement and reference signals which are selected based on high signal to noise ratio and cor rela tion coefficient.The calculation results show that there is a highly linear relationship between the measured and actual CO con centrations,and the linearity is 0.9995over the whole tested range.A detection limit of 37.3ppm is achieved. The standard deviation of 0.839% is obtained using 30successive measurements with each measurement time of~10s durin g 30min,which demonstrates the good stability of the system.