With the improvement of Chinas economic development and peoples living standards,the functional food is more and more demand by people.An excellent source of lycopene and other functional substance is watermelon.Therefore,the watermelon breeding and human health will be vastly promoted by the research on lycopene in watermelon.According to our study,some results were found as follows:(1)The lycopene content increased during watermelon fruit development(10 days to 30 days after pollination),riper fruits had higher lycopene content than less ripe fruits.Diploid watermelon developed fast and accumulated more lycopene at the early stage,the lycopene contents of triploid and tetraploid watermelon started to increase on 20 days after pollination,then increased faster and were higher than that of diploid on 30 d after pollination.(2)Lycopene contents and expression of five key genes(PSY,PDS,ZDS,CRTISO,LCYb)during watermelon fruit development were measured.The expression of PSY in five genes was the highest in fruit whole growth period.The expression of LCYb in red flesh watermelon was the lowest in all genes,especially at 25d after pollination,while its expression in the yellow flesh watermelon was lower than that of PSY,this suggests the importance of LCYb in color control and lycopene synthesis.The highest expression of all five genes in the root,stem and leaf were almost appeared on flowering period.And only the PSY expression in diploid was higher than polyploidy,the expression of other genes in diploid were lower than polyploidy.In conclusion,our studies suggested that there were differences in lycopene content change among different ploidy watermelon.