Raman spectroscopy was nondestructive and rapid method for the determination of substance composition. In order to improve the sensitivity of monitoring, the cavity-enhanced spontaneous Raman scattering of 408nm band semiconductor laser was studied. 408nm semiconductor laser with output power of 500mW and linewidth of 0.9nm was used as excitation light. The laser was coupled into confocal spherical mirror cavity. The reflectivity of two-sided confocal spherical mirrors was 96.5% and 99.5%, respectively. Some lasers returned to the semiconductor laser to form optical feedback. Semiconductor laser resonated with confocal cavity. The optical feedback process of the device was discussed. The mode matching and frequency matching of the external cavity were analyzed respectively. The results show that, the power in the confocal cavity reaches 15W. The power is increased by 30 times. Raman signals are collected with 90° probe configuration. Air Raman signal detection has been completed. 900 counts of N2 signal are obtained in 1s integration time. The results show that the resonance enhanced cavity greatly enhances the Raman scattering signal and has the potential to be used in the on-line detection or high-sensitivity detection of a variety of gases.