Endoscopy is the main method in the clinical diagnosis and treatment of gastrointestinal diseases. Its function is to obtain the structural information of the tissue. The occurrence and development of digestive diseases are usually accompanied by the changes of functional information， such as blood oxygen and metabolic parameters. This paper develops a fiber optic endoscopy system based on endogenous optical signal imaging technology， which can measure changes of six types of functional information including biological tissue oxy-hemoglobin， deoxy-hemoglobin， cytochrome C， cytochrome oxidase， FAD and scattering characteristics for biological tissues. In this study， we designed an in-vivo animal experiment with injection of excessive sodium nitrite. Then， the designed fiber optic endoscopy system was utilized to obtain the blood oxygen and metabolism related parameters in the same field at 3， 6， 9， 12， 15 and 18 min time points during drug injection. The concentration of oxyhemoglobin in the experimental model continued to decrease， while that of deoxyhemoglobin continued to increase. Research shows that the fiber optic endoscopy system based on intrinsic optical signal can accurately reflect the change of biological tissue function information.