We chose the cotyledous of cucurbit seedlings during first real leaf emerged as explant. KT 1.0 mg/L as a ideal hormone treatment in which a floral experimental system of cucurbit cotyledon was established in vitro. This system showed good repeat and higher ratio of floral bud differentiation (60%). The content of endogenous GA1/3 in the cotyledons is lower during first real leaf of cucurbit seedlings, but ZRs increased significantly, meanwhile ZRs/GA1/3 ABA/GA1/3 Spd/Put Spm/Put showed higher ratio which benefit floral bud differenfiation of cotyledons. So that it is ideal seedlings age to cut cotyledon during first real leaf emerged of cucurbit seedlings.