Measurement of trace-gas vertical profile is very important for research of atmospheric pollution. The multi-axis differential optical absorption spectroscopy (MAX-DOAS) is used on trace-gas profile monitoring. Combing with radiative transfer models, trace gas vertical profile is derived from slant column densities of several elevation angles of MAX-DOAS with optimal estimation method. The parameters setup of retrieval algorithm and the characterization of the retrieval has been described in detail. MAX-DOAS is used to monitor NO2 profile of Hefei area. The measurement result is validated with long-path differential optical absorption spectroscopy (LP-DOAS), and the correlation coefficient is 0.80. This technique provides a simple and convenient method three-dimensional observation for air pollution.