With the speed up of industrialization process, NO2 generated by vehicles, power plants emissions and other human factors is increasing. Since NO2 not only plays important role in the formation of ozone, which also causes the formation of acid rain, the detection of NO2 concentration if of great significance among many areas. In this paper, to detent NO2, experiments and comparisons are done to the different frequency by two kinds of sensors. The sensing signal of SAW sensor if the elastic wave along the surface of the objects, while the sensing signal of the magnetoelastic sensor comes from the external magnetic field force on the magnetoelastic material, but response signals of both two sensors are frequency shift, which use the network analyzer to detect. The preliminary experiments results show that with the NO2 adsorption, the frequency response of magnetoelastic sensor is obvious than the SAW sensor, which owes more practical significance of research in related fields.