The concentration of exhaled CO as a biomarker for certain diseases has attracted significant attention. However， existing CO concentration detectors suffer from low sensitivity and slow response times. To address this， we developed a high-sensitivity， rapid-response exhaled CO measurement system based on absorption spectroscopy， utilizing a quantum cascade laser with a central wavelength of 4.59 μm and a 3.8 m multi-pass cell. The CO concentration was analyzed using both direct absorption spectroscopy （DAS） and wavelength modulation spectroscopy （WMS）. The DAS method demonstrated a linearity of 0.998 with a detection limit of 3.68 × 10??. For WMS， the linearity remained 0.998 at CO concentrations below 6.00 × 10??， achieving a detection limit of 3.00 × 10??. Through Allan variance analysis， optimal integration times of 170 s for DAS and 250 s for WMS were determined， corresponding to improved detection limits of 2.00 × 10?? and 3.00 × 10?1?， respectively. Finally， exhaled CO concentrations from 14 volunteers were measured， demonstrating the system''s capability to distinguish between smokers and non-smokers. This provides a scientifically validated tool for assessing smoking status in clinical smoking cessation programs.