The size of seed is an important factor affecting litchi fruit quality.Seed abortion(chicken tougue)is a common heredity phenomenon during litchi fruit development.Seed abortive fruits not only have higher flesh recovery but also better flavor.Currently almost all valuable litchi cultivars are characterized with high abortion rate.However,the mechanism of litchi seed abortion is poor-documented.In this study,three different seed development type cultivars were used as materials to investigate the function of cell wall invertase in seed development.The main results were as follows:Reduced activity of cell wall acid invertase(CWAI)was the main cause for the block of litchi liquid endosperm development.Much lower activities of CWAI were detected in the seed funicle and seed coat in liquid endosperm reduced cultivarNuomicithan liquid endosperm rich cultivars Feizixao and Heiye.CWAI silence resulted in reducing liquid endosperm and therefore enhancing seed abortion.Two CWAI genes(LcCWAI2 and LcCWAI5)and one CWAI inhibitor(LcCIF)were targeted as the main genes in control the activity of CWAI.VIGS experimental system was set up in litchi to test the function of these genes in litchi seed development.LcCWAI silence resulted in seed abortion in normal cultivars,while LcCIF silence favored endosperm development and fruit set in abortive cultivar.These results suggested that the decrease CWAI activity in the funicle and seed coat of litchi cultivar Nuomici was the main reason for the retarding endosperm development and then seed abortion either through reducing the import of carbohydrates to the symplastic isolated filial tissue and/or sugar signaling.And the decrease CWAI activity might derive from the much high expression of CWAI inhibitor.