Abstract: 【Objective】The study was to investigate the effects of preharvest flower-and-fruit thinning on the harvest quality and postharvest storability of longan（Dimocarpus longan Lour.）fruit, and the synergistic effect of selenium（Se）supplementation on it.【Methods】With Longan fruit cv. Shixia as the material, 3 treatments were designed: control（TR-A, no thinning）, flower-and-fruit thinning（TR-B）, TR-B plus Se-fertilizer treatment（TR-C），and 3 blocks were repeated. The fruit harvest quality among different treatments and blocks and postharvest storability at 5℃ were compared.【Results】At harvest, for the longan fruits treated with thinning（TR-B）, the single fruit mass, size, apparent chroma quality and TSS content of longan fruit increased by 19.66%, 7.54%, -7.24%（a*value）and 8.62%, respectively. The fruit harvest quality of TR-C was better than that of the control（TR-A）, but its synergistic effect was not obvious. After storage, TR-B significantly improved the storability of longan fruit stored at 5℃（P ＜ 0.05）, featured with pericarp browning index（35 d）and pulp autolysis index（51 d）decreasing by 28.26% and 71.67%, respectively. However, the synergistic effect of TR-C was not obvious. During storage, TR-B fruit maintained better appearance quality with more yellowish green, TR-C tended to be brown, while TR-A tended to be dark brown. The results of multivariate analysis of variance showed that the storability of longan fruit among different treatments was significant with P ＝ 0.016, 0.032 and 0.002 below 0.05 resulted from three multivariable tests, while not significant between 3 blocks. The indicators with significant effects between treatments included pericarp browning index, pulp autolysis index, b* value during storage and single fruit mass; and the indicators with significant effects between blocks included b* value and C* value during storage.【Conclusion】The effect of flower-and-fruit thinning on the harvest quality and storability of longan fruit was the best, but the synergistic effect of Se-supplement treatment was not obvious, and block setting had no significant impact on the fruit properties with different treatments. So, flower-and-fruit thinning is an important measure to improve the harvest and storage quality of longan fruit.