Aiming at the problems of weak Raman spectrum signal and long detection time of weakly scattered samples, a fast laser confocal Raman spectrum detection method based on Crop Mode is proposed. The method reduces the exposure time by reducing the signal transmission unit, and only collects the effective Raman spot area of the signal target unit. On the basis of guaranteeing the intensity of Raman signal, the signal-to-noise ratio of Raman spectral is also improved to reduce the required detection time and realize fast Raman spectral imaging of weakly scattered samples. Experiments show that compared with the traditional confocal Raman spectral detection system, the Crop mode adopted in this paper can improve the imaging speed of confocal Raman spectrum by more than 60 times, which provides a new technical way for the rapid detection of confocal Raman spectral microscopy technology.