A fiber-optic Raman spectrum sensor system is used for the fast diagnosis of esophageal cancer during clinical endoscopic examination. The system contains a 785 nm exciting laser, a Raman fiber-optic probe with 7 large core fibers and a focus lens, and a highly sensitive spectrum meter. The Raman spectrum of the tissue could be obtained within 1 second by using such a system. A signal baseline removal and denoising technology is used to improve the signal quality. A novel signal feature extraction method for differentiating the normal and esophageal cancer tissues is proposed, based on the differences in half-height width (HHW) in 1200 cm^-1 to 1400 cm^-1 frequency band and the ratios of the spectral integral energy between 1600 cm^-1 - 1700 cm^-1 and 1500 cm^-1 - 1600 cm^-1 band. It shows a high specificity and effectivity for the diagnosis of esophageal cancer.