The response of photosynthesis rate to light intensity and CO₂ concenrtration in 6 varieties were measured with Licor-6400 in the sixth year after being planted. The results indicated that exponential equation was fitted for these responses. Characteristic parameters calculated from those exponential equations were found to differ significantly among different varieties. Two of the varieties, Ameristand201+ Z and Lobo, may possess high yield potential as they displayed higher light saturation estimate (Lk), apparent quantum yield (AQY), carboxylation efficiency(CE) and lower CO₂ compensation point(CCP), compared with the remaining varieties. Fall dormancy level had negative correlations with AQY, CE, light compensation point(LCP), Lk, dark respiration rate(R_d ) and photorespiration rate (R_p), while insignificant positive correlation was observed with CCP and CO₂ saturation point(CSP ).