private DataTable dt = new DataTable("ResultTable");

        public frmMain()
        {
            InitializeComponent();

            dt.Columns.Add("列1", typeof(string));
            dt.Columns.Add("列2", typeof(string));
            dt.Columns.Add("列3", typeof(string));
        }

        private void frmMain_Load(object sender, EventArgs e)
        {
            dataGridMain.DataSource = dt;

            DataGridTableStyle dgts = new DataGridTableStyle();
            dgts.MappingName = dt.TableName;

            DataGridTextBoxColumn dgtbc = new DataGridTextBoxColumn();
            dgtbc.HeaderText = dt.Columns[0].ColumnName;
            dgtbc.MappingName = dt.Columns[0].ColumnName;
            dgtbc.Width = (int)(0.15 * (dataGridMain.Width - 4));
            dgts.GridColumnStyles.Add(dgtbc);

            DataGridTextBoxColumn dgtbc2 = new DataGridTextBoxColumn();
            dgtbc2.HeaderText = dt.Columns[1].ColumnName;
            dgtbc2.MappingName = dt.Columns[1].ColumnName;
            dgtbc2.Width = (int)(0.15 * (dataGridMain.Width - 4));
            dgts.GridColumnStyles.Add(dgtbc2);

            DataGridTextBoxColumn dgtbc3 = new DataGridTextBoxColumn();
            dgtbc3.HeaderText = dt.Columns[2].ColumnName;
            dgtbc3.MappingName = dt.Columns[2].ColumnName;
            dgtbc3.Width = (int)(0.7 * (dataGridMain.Width - 4));
            dgts.GridColumnStyles.Add(dgtbc3);

            dataGridMain.TableStyles.Add(dgts);
        }

大家自己看吧 ，可以调节DataGrid的列宽了，哈哈～