Photosynthesis is the basis for plant survival. Leaf color mutants are often accompanied by abnormal chloroplast structure and blocked photosynthetic pigment synthesis. Therefore， the study of leaf color mutants can provide experimental data and theoretical support for photosynthesis and photomorphogenesis. In this study， maize etiolation mutant et9， which was identified from maize inbred line PH6WC treated by 2.48 Gy fast neutron irradiation， was used as the material. Through phenotypic identification， determination of chlorophyll content in leaves， microscopic observation of chloroplast structure and analysis of photosynthetic characteristics， plant height and panicle height of et9 plants were very significantly lower than those of the wild type. The flag leaf length， flag leaf width and the third leaf width were very significantly reduced in mutant. The tasseling， pollen shedding and silking stages were delayed by 10-12 days compared with the wild type. The contents of chlorophyll a， chlorophyll b and total chlorophyll were obviously lower than those of the wild type. The chloroplast structure is loose， the distribution of thylakoids is chaotic， and the number of basal grains is small. In contrast to the wild type， the net photosynthetic rate， stomatal conductance and transpiration rate decreased significantly， while the intercellular carbon dioxide concentration increased significantly. The chloroplast fluorescence parameters were significantly lower than those of the wild type except for photochemical quenching. Genetic segregation analysis revealed that the yellowing phenotype was controlled by a nuclear recessive gene， named Zmet9. The F₂ segregating population was generated by crossing it with maize inbred line B73， and the mutation site was initially located in the 20-22 Mb on chromosome 9 of maize using the BSR-seq method. Four KASP markers and two InDel markers were further developed in the initial mapping interval， and about 1100 plants showing mutant phenotype were used for fine mapping. Finally， Zmet9 was finely mapped to a region of about 160 kb between markers KASP19 and 2040. This interval contains five annotated candidate genes， of which Zm00001d045384 encodes an iron superoxide dismutase. Considering that mutation of its homologous genes FSD2 and FSD3 in Arabidopsis shows leaf color bleaching phenotype， we speculate that Zm00001d045384 may be a candidate gene for Zmet9.