To analyze the hybrid vigor between parent and hybrid plants, three cucumber cultivars were used (Parents: A, B; F1 hybrid: C). Continuous observations and destructive samplings were made throughout the growth of plants. Experimental results indicate that cyclic changes occur in the dry weights of organs (internode, leaf and petiole) of different positions along the stem. The yield, organ sizes and fruit numbers of the three cultivars were different. To analyze these differences, a Functional-structural model 'Greenlab' was applied to compute the parameters of source sink for organs. The results demonstrate that plant architecture plays an important role in heterosis breeding. This study is a first step to build a tool to provide the guidance of heterosis breeding for breeders on cucumber.