There are too many articles about diagnosing cancers by the content of tumor chemical signs in plasma, but there are few articles about diagnosing them by spectroscopy. The present article belongs to the few. The authors can differentiate the normal and malignant esophagus by the statistic and analysis of absorption spectra after their plasmas are detected by spectrophotometry, which provide a new approach to quickly diagnosing malignant esophagus.