Abstract: Phenological observation was done for eight mature trees of Liriodendron.Stages order from early to late in sprout,bud and leaf growth was L.tulipifera×L.chinense,L.tulipifera,L.chinense×L.tulipifera and L.chinense,successively.Leaf growth rate of L.chinense×L.tulipifera was faster than the others.Flowering time of hybrid was longer than their parents made hybrid trees have longer time for flower view and admire.And the overlapping period of all trees investigated was twentyone days,increased the chance for crossing with each other.Diurnal change of net photosynthetic rate was different among seedlings of four families of reciprocal crosses and one of L.chinense.The curve of diurnal change of net photosynthetic rate of back cross family seedlings was single peak,and decreasing slowly.Those curves of L.chinense×L.tulipifera and those from crossing between first generation hybrid trees were double peaks,and L.tulipifera×L.chinense single peak but decreasing rapidly.Family order from high to low rate of net photosynthesis was back cross,L.chinense×L. tulipifera,L. tulipifera×L. chinense,L.chinense,crossing between first generation hybrid trees,successively.Net photosynthetic rate of most families was differently correlated to the concentration of CO2,transpiration,air and leaf temperature,effective radiation of photosynthesis closely.And family seedlings from L.tulipifera×L.chinense had some special characters,all stages in sprout,bud and leaf growth,flowering were the earliest,and flowering time the longest,net photosynthetic rate of seedling was not correlated with concentration of CO2.