Abstract:To find the variation of growth and photosynthetic traits and discuss the most important assistant factor for breeding selection of Betula platyphylla,6 half-sib families of were taken in the research,we measured and analyzed 24 profiles of the B.platyphylla half-sib families.The analysis of variance calculation show that:(1)There was a remarkable difference in height (H),basic diameter (BD),leaf length (LL),leaf width (LW),leaf number (LN),the ratio of leaf length to width (L/W),net photosynthesis rate (Pn),stomatal conductance (Gs),intercellular CO2 concentration (Ci),transpiration rate (Tr) and water use efficiency (WUE).The coefficients of variation and genetic variation of H,BD,LL,LW,LN,L/W,Pn,Gs,Tr and WUE were more than 10%.(2)There were also exist remarkable difference in the chlorophyll fluorescence parameters (F0,F0′,Fs,Fv′/Fm′,NPQ) and Yield.Except parameter NPQ,the coefficients of variation and the genetic variation of chlorophyll fluorescence parameters were less than 10%.(3)The heritability of chlorophyll fluorescence parameters of B.platyphylla half-sib families were higher than 0.4,but the photosynthetic and growth parameters were higher than 0.7,indicating that B.platyphylla half-sib families variation was strongly controlled by genetic factors.(4)The results of phenotypic correlation showed that there were significant positive correlation among the growth traits and WUE,but negative correlation with Yield.Regression analysis results showed that LW and LN were the first two variables introduced for H and BD equations,indicating that LW and LN were very important parameters for B.platyphylla seedling selection and evaluation.