Abstract: In order to explore the adaptability of introduced Magnolia dawsoniana during summer high temperature period in Chengdu, the photosynthetic indexes and chlorophyll content of four kinds of M. dawsoniana seedlings were measured under natural summer high temperature conditions in Chengdu Plain. The results showed that (1) the diurnal variation of net photosynthetic rate of the four kinds of M. dawsoniana seedlings was bimodal, with obvious midday depression of photosynthesis. The daily average net photosynthesis rate of grafed Magnolia dawsoniana seedlings was the largest. The diurnal variation of transpiration rate of the four kinds of seedlings was also bimodal, and the daily average transpiration rate of grafted Magnolia sieboldii seedlings was the largest. (2) The stomatal conductance of the four kinds of seedlings decreased obviously during the high noon temperature period, and after the high noon temperature period, the stomatal conductance of seedlings of Magnolia sieboldii showed the largest increase. Stomatal closure limited the photosynthetic rate during high temperature at noon, while in the evening, the decrease of light intensity made the photosynthetic rate decrease. (3) The correlation between the net photosynthetic rate of M. dawsoniana seedlings and environmental factors was highly consistent. (4) The order of chlorophyll content of the four kinds of seedlings was grafted Magnolia dawsoniana seedlings > Michelia alba seedlings > real seedlings > Magnolia liliiflora seedlings. Photosynthetic rate of four kinds of M. dawsoniana seedlings was inhibited under high temperature stress. The net photosynthetic rate and chlorophyll content of grafted Magnolia dawsoniana seedlings were the highest, and the adaptability was better, while the adaptability of real Magnolia dawsoniana seedlings was worse.