Light-emitting diode (LED) is a promising new type of light source for differential optical absorption spectroscopy (DOAS). Fabry-Perot etalon structures in the emission spectrum of some LED, however, influence DOAS retrievals. The cause of emergence of these structures in a blue LED (Luxeon, LXHL-LR3C) and the relation between them and the angle of incidence are analyzed. The emission spectrum of LED may become smooth by tilting the LED in the fiber coupling so as to remove the etalon structures. Long-path DOAS measurements on atmospheric NO2 are carried out with the LED with four different angles of incidence and the measurement results are compared with these of conventional long-path DOAS with an arc lamp. The results show that NO2 concentrations are in very good agreement with one another when tilting angle is 30°. The detection limit of long-path DOAS measurements with the LED is only about 13% of that without tilting LED. These prove that if selected angle of incidence is so appropriate that the spectrum of LED becomes smooth, the influence of etalon structures of LED on DOAS retrievals can be effectively removed.