Tham khảo cách Thêm thẻ html

public static MvcHtmlString CheckBoxListFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, IEnumerable<TProperty>>> expression,
    IEnumerable<SelectListItem> multiSelectList,
    Object htmlAttributes = null)
{
    // Derive property name for checkbox name
    var body = expression.Body as MemberExpression;
    if (body == null)
        return null;

    String propertyName = body.Member.Name;

    // Get currently select values from the ViewData model
    IEnumerable<TProperty> list = expression.Compile().Invoke(htmlHelper.ViewData.Model);

    // Convert selected value list to a List<String> for easy manipulation
    var selectedValues = new List<String>();

    if (list != null)
        selectedValues = new List<TProperty>(list).ConvertAll(i => i.ToString());

    // Create div
    var ulTag = new TagBuilder("ul");
    ulTag.AddCssClass("checkBoxList");
    ulTag.MergeAttributes(new RouteValueDictionary(htmlAttributes), true);

    // Add checkboxes
    foreach (var item in multiSelectList)
    {
        ulTag.InnerHtml += String.Format(
            "<li><input type=\"checkbox\" name=\"{0}\" id=\"{0}_{1}\" value=\"{1}\" {2} /><label for=\"{0}_{1}\">{3}</label></li>",
            propertyName,
            item.Value,
            selectedValues.Contains(item.Value) ? "checked=\"checked\"" : "",
            item.Text);
    }

    return MvcHtmlString.Create(ulTag.ToString());
}