Abstract: Wild-type P31of tomato and yellowing mutant WAX-7obtained by ethyl methyl sulfone（EMS） mutagenesis were used as the main materials.Main morphological characteristics,leaf photosynthetic pigment content,photosynthetic parameters,and relative expression levels of chlorophyll synthesis and metabolism related genes between mutant and wild type were measured with method of comparison in seedling stage,in order to reveal the mechanisms underlying leaf color variation in tomato yellow mutants.The results showed which compared with the wild type,the mutant WAX-7 showed yellow leaves,the plant height,internode length and leaf area were significantly reduced.The contents of chlorophyll a,chlorophyll b,carotenoids and total chlorophyll in the leaves of the mutant were significantly lower than those of the wild type.In addition,the photosynthetic rate,intercellular carbon dioxide concentration and stomatal conductance of the mutant leaves were significantly or extremely significantly lower than those of the wild type.The relative expression levels of chlorophyll synthesis key genes SLPOR,SLCAO1,and SLCHLH in mutant leaves were also significantly or extremely significantly lower than those of wild type,but the relative expression of chlorophyll degradation key gene SLPPH was significantly higher than that of wild type.