MicroRNAs (miRNAs) are versatile regulators of gene expression at both the transcription and post-transcription levels. The microRNA miR396 plays vital roles in growth, development, and resistance to abiotic stresses in many plant species. However, the roles and functions of miR396 in soybeans are not well understood. Here, we report that Gm-miR396a influences soybean development and salinity tolerance. We found that soybean miR396a was responsive to salt stress. Gm-miR396a gene-edited lines (miR396a-GEs), created using CRISPR/Cas9, exhibited more branches, higher grain yields, and greater salinity tolerance than control plants. The transcripts in lines with altered abundance of miR396a-GE were significantly enriched for biological processes related to hormone regulation. Overexpression of the Gm-miR396a precursor (pre-miR396a-OE) resulted in developmental deficiencies including dwarfness, abnormal inflorescences and flowers, smaller and fewer seeds, and small leaves with larger and more numerous stomata. Transcriptome analysis indicated photosynthesis-related genes were downregulated in pre-miR396a-OE plants. These results contribute valuable insights into the function of Gm-miR396a in soybeans and hold promise for enhancing soybean yield and salinity tolerance through germplasm innovation.