Taking male，female and hermaphrodite flower of 3 kinds of watermelon（Citrullus lanatus）sexual type as material， we made these flower buds at different development stages into paraffin section for cytomorphological observation．The result showed that the floral primordial processes of these 3 kinds of sexual type from watermelon had no visible differences. At the end of hermaphroditic stage，the length of flower bud was about 0.8-1.0 mm and the differentiation development of male，female and hermaphrodite flower began. Stamen primordia volume of male and hermaphrodite flower augmented rapidly，and carpel primordia of female and hermaphrodite flower began to differentiate into stigma and ovary．In deformity female flower，the base of carpel primordia would stop the development after denting to a certain degree，while the stamen primordia would not stop elongation and continue to develop to form the mature stamen with small amount of mature pollen grains.