The applicability and application of modern light emitting diodes (LEDs) as active source in differential optical absorption spectroscopy (DOAS) was discussed in this paper. The radiative properties of LEDs and spectral shape，spectral range，spectral stability were analyzed. When temperature was not constant，the Fabry Perot etalon structures of LEDs would interfered with the DOAS evaluation. If they were treated as a kind of ‘component' of atmosphere and retrieved with other atmospheric components together，their effect on the measurements could be restricted to a minimum. The experimental results showed that LEDs can be used successfully as light sources in active DOAS to measure NO2 in the atmosphere. The correlation of the NO2 concentration measured by the LEDs-DOAS and the xenon arc light DOAS was 0.99. The detection limits of 1.1×10-9 were obtained for the path length of a 0.7km in the atmosphere.