private static object GetPropertyValue(object obj, string property)
{
  System.Reflection.PropertyInfo propertyInfo = obj.GetType().GetProperty(property);
  return propertyInfo.GetValue(obj, null);
} 
var resultList = sortOrder == "desc" ? groupList.OrderByDescending(p => GetPropertyValue(p, sortName)) : groupList.OrderBy(p => GetPropertyValue(p, sortName));
//linq方式：
//
var resultList1 = from p in groupList orderby GetPropertyValue(p, m.SortName) select p;
if (sortOrder == "desc")
 resultList1 = from p in groupList orderby GetPropertyValue(p, sortName) descending select p;

var groupQueryList = groupList.AsQueryable();//here
var tmpList = groupQueryList.OrderBy(sortName, sortOrder);

public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
{
  return ApplyOrder<T>(source, property, "OrderByDescending");
}
public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
{
  return ApplyOrder<T>(source, property, "ThenBy");
}
public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
{
  return ApplyOrder<T>(source, property, "ThenByDescending");
}
static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName) {
  string[] props = property.Split('.');
  Type type = typeof(T);
  ParameterExpression arg = Expression.Parameter(type, "x");
  Expression expr = arg;
  foreach(string prop in props) {
   // use reflection (not ComponentModel) to mirror LINQ
   PropertyInfo pi = type.GetProperty(prop);
   expr = Expression.Property(expr, pi);
   type = pi.PropertyType;
  }
  Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
  LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
  object result = typeof(Queryable).GetMethods().Single(
    method => method.Name == methodName
      && method.IsGenericMethodDefinition
      && method.GetGenericArguments().Length == 2
      && method.GetParameters().Length == 2)
    .MakeGenericMethod(typeof(T), type)
    .Invoke(null, new object[] {source, lambda});
  return (IOrderedQueryable<T>)result;
}