Abstract: 【OBJECTIVE】One of interesting novel phenomenon on grafting observed in the melon is the weak growth vigor in the initial stage after planting. However, in the middle and late stage, the growth vigor is becoming enhanced and ultimately better than own-root seeding. 【METHOD】In order to understand the mechanism underneath, Pumpkin ‘Shengzhan No.1’ was used as rootstock for melon ‘Jinmi’ in this experiment, and the own-root seedling was used as control. Effects of grafting on chlorophyll fluorescence parameters were investigated with PAM-2100 chlorophyll fluorometer in different periods after planting (20, 30, 45 and 60 days). 【RESULT】The results showed that the maximum photochemical efficiency (Fv/Fm), quantum efficiency of PSII photochemistry (ΦPSⅡ), the electronic transfer rate (ETR), the photochemical quenching (qP) of the grafted seedling were lower than those of the own-root seedling in the 20 days after planting. However, PSⅡ efficient photochemical quantum yield (Fv’/Fm’), Fv/Fm, ΦPSⅡ, ETR , qP were all obviously higher in the 30, 45 and 60 days. But the non-photochemical quenching (qN) of the grafted seedling was lower than the control. The energy distribution in photochemistry (θPSⅡ) was lower in the 20 days, but higher in the 30 days. θPSⅡ of grafted seedling exceeded 70% in the 45 days, yet the control was only 60%.【CONCLUSION】In the initial stage after planting, the light energy transferring and translating efficiency of the grafted seedling was lower than the control. But the efficiency increased clearly after the 30 days. The research indicated that the grafted melon grew mostly in middle and late period, and led better growth vigor finally.