The fruits of Cornus officinalis in different developmental stages were selected as the research object. The distribution and accumulation of tannin during the development of C. officinalis fruit were studied by means of fruit morphology observation, microscopic and ultramicro technology, histochemical localization and ultraviolet spectrophotometer, and the difference of tannin content in different development stages was tested by single factor ANOVA. The purpose is to provide theoretical basis for the study of tannin in the development of C. officinalis fruit. The results showed that: (1) there are obvious changes in peel color and fruit volume during the fruit development of C. officinalis, which can be divided into three stages: young fruit stage, middle fruit stage and mature fruit stage. Tannin was mainly distributed in the tannin cells of the pericarp of C. officinalis fruit. (2) During the fruit development, the number of tannin cells increased at first and then decreased. In the young fruit stage, the number of tannin cells increased with the fruit development, and began to decrease in the middle fruit stage. (3) The change trend of tannin content in line with the number of tannin cells changed, and the tannin content reached the maximum at 120 days after anthesis, and then decreased gradually. (4) Tannins first accumulated in the small vacuoles of cytoplasm, and then the central vacuole was the main place where tannins accumulate. Tannins mainly have three accumulation forms: granular, irregular and plate. Tannin cells have more mitochondria. In the late middle fruit stage and mature fruit stage, electron dense substances accumulated near the vacuole membrane of the central vacuole. It is considered that the mesocarp parenchyma cells in C. officinalis fruit are the exclusive cells for tannin accumulation, the synthesis and transportation of tannin are closely related to vacuoles, vesicles and mitochondria. The astringency of fruits and the total tannin content decrease at mature stage, and the dynamic change of tannin accumulation is closely related to the adaptability of plants to the environment and the astringency of fruits. The synthesis mechanism of tannin in C. officinalis fruit can be further studied by combining metabolomics and transcriptome methods.