A scanning narrowband coherent anti-stokes Raman scattering (CARS) spectrometry was built up for the detection of the production of a variety of hydrocarbon components in the methanol to olefins (MTO) process. Methane, ethane, ethylene, propylene CARS spectra were scanned using this spectrometry; the characteristic Raman spectrum of each molecule was obtained. Under the same conditions, the relationships between CARS signal energy and different target molecules and other background gases were studied. A simplified model was established to simulate the CARS signal characteristic peak intensity contributed with different molecules, and the concentrations of Raman active molecules were calculated by this mode. This paper proposed a method of the on-line detection of Raman-active gas concentration by time-sharing narrowband CARS spectra. This method may have practical applications in the online analysis of catalytic chemical industry. The experimental error for the detection of the concentration of methanol, ethylene and propylene is less than 9%.