Leaf color mutant is an ideal material for analyzing plant photosynthesis mechanism.Agronomic traits,photosynthetic pigment content,photosynthetic parameters and chloroplast ultrastructure of wheat mutant LF2090 with yellow green-revertible flag leaf were investigated,while the wild type H261 was selected as control.The results showed that the content of chlorophyll-b in mutant had a significant reduction in the flag leaf yellowing period,the number of chloroplasts and grana were also reduced,but photosynthetic rate did not change significantly.While,the pigment content,CO₂ concentration and photosynthetic rate of the mutant all dropped dramatically in the flag leaf green-revertible stage and most of grana in the chloroplast were disappeared,however,the relative content of chlorophyll-b was increased.The close of stomatas in the LF2090’s flag leaf is the main reason to reduce the photosynthesis rate and the index of agronomic traits;the decrease of pigment content,which resulted in the abnormal chloroplast structure,also affects the photosynthetic rate.The change of proportion between chlorophyll-a and chlorophyll-b causes leaf color change from yellow to green.