方法一屬性

<asp:CheckBoxList ID="CheckBoxList1" runat="server" RepeatDirection="Horizontal">
            </asp:CheckBoxList>
//可選水平或豎直

方法二點選選擇

點選CheckBox時，排列方式為水平

    protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
    {
        this.CheckBoxList1.RepeatDirection = RepeatDirection.Horizontal;
        this.CheckBoxList1.RepeatColumns = 3;  //每行的個數
    }