In this study, we systematically investigated the ultrastructure of the phloem and surrounding parenchyma cells using transmission electron microscopy during the development process of Xanthoceras sorbifolium Bunge fruit, to understand the unloading pathway and mechanism during the fruit development. The results showed: (1) during the fruit development process, the cell cavity of the sieve element (SE) was empty and few organelles exited, but there were some vesiclelike and microfibrillike structures in SE. With increase of cytoplasm density and organelles abundance, the degree of vacuolization in companion cell (CC) varied, and most of them had multiple small vacuoles; Phloem parenchyma cell (PP) had large central vacuoles, and vesicle transport occurred in the middle stage of development. They were rich in organelles such as mitochondria, golgi bodies and endoplasmic reticulum, which degraded at the later stage of development. This indicated that the metabolism and substances transport in fruit decreased gradually with the fruit development. (2) During the development of fruit, there were always some plasmodesmata between SE and CC, and lots of plasmodesmata between CC. However, only a certain number of plasmodesmata existed between the SECC complex and PP at the early and late stage of fruit development, but almost no plasmodesmata existed at the middle stage of fruit development. Based on the above results, we concluded that the unloading pathway of assimilate changed from symplastic to apoplastic and then to symplastic during the fruit development.