Mutant is an important material for gene discovery and function research as well as crop improvement in plants. In this study, we reported the characterization of an ideal plant-architecture mutant (it1) from our EMS mutant population derived from the soybean cv. Zhongpin661 (Zp661). Phenotypic analysis revealed that the it1 mutant, compared with the wild type plant, showed more compacting plant architecture, eg, shorter internodes, and darker green leaves. And also the mutant showed a significant decrease in plant height by 30% compared to that of the parental line Zp661, but no significant difference in internode number, indicating that lower plant height for it1 is mainly caused by shortened internode length. Meanwhile, numbers of agronomic traits of the it1 mutant including number of branches, number of pods, petiole length and angle, 100-seed weight and yield per plant all displayed a significant or very extremely significant decline than the wild parent. In addition, the physiological characteristics were determined under normal growth conditions in the field, and it1 displayed significantly higher chlorophyll content and cellulose-lignin component than the wild type in seed-filling period. Therefore, the identification of the it1 mutant provides excellent material for mapping, cloning and function research of plant architecture-related genes and genetic improvement in soybean.