Differential optical absorption spectroscopy （DOAS） has become a widely used method for the simulataneous detection of atmospheric trace gases with low detection limits. DOAS method is proposed for monitoring the vertical distribution of atmospheric trace gases . Based on DOAS technique and a high tower with angle-reflectors, the scanning long-path(LP)-DOAS system is developed . Field observations of vertical distribution of NO2 was performed by using the scanning LP-DOAS system in the summer of 2007. The NO2 concentrations along three light paths were accurately measured, and the detection limits along three light paths and the total systematic error were obtained. The vertical profiles and vertical gradient of NO2 were successfully retrieved by using the vertical profiles model. The results indicate that the scanning LP-DOAS system can perform vertical observations of trace gases in the urban boundary layer.