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 (etiolation 9), which was screened from maize inbred line PH6WC by 2.48Gy 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, et9 plant height and panicle height were significantly lower than those of the wild type, and the flag leaf length, flag leaf width and the third leaf width were significantly reduced. 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 wild type. The chloroplast structure is loose, the distribution of thylakoids is chaotic, and the number of basal grains is small; Compared with 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 pattern analysis revealed that the yellowing phenotype was controlled by a nuclear recessive gene, named Zmet9 (Zea mays etiolation 9). The F2 segregating population was constructed by crossing it with maize inbred line B73, and the mutation site was preliminarily located in the 2 Mb region of 20 - 22 Mb on chromosome 9 of maize using the BSR-seq method. Four pairs of KASP markers and two pairs of InDel markers were further developed in the initial mapping interval, and about 1100 mutant phenotypic plants were used for fine mapping. Finally, Zmet9 was finely mapped to a region of about 160 kb between KASP19 and 2040 on chromosome 9 of maize. This interval contains five candidate genes, of which Zm00001d045384 encodes an iron superoxide dismutase, and the leaf color bleaching phenotype occurs after the mutation of homologous genes FSD2 and FSD3 in Arabidopsis. We speculate that Zm00001d045384 may be a candidate gene for Zmet9.