public IList<DependencyProperty> GetAttachedProperties(DependencyObject obj)
{
    List<DependencyProperty> result = new List<DependencyProperty>();
 
    foreach (PropertyDescriptor pd in TypeDescriptor.GetProperties(obj,new Attribute[] { new PropertyFilterAttribute(PropertyFilterOptions.All) }))
    {
        DependencyPropertyDescriptor dpd =
            DependencyPropertyDescriptor.FromProperty(pd);
 
        if (dpd != null)
        {
            result.Add(dpd.DependencyProperty);
        }
    }
 
    return result;
}

在这里找到：http://social.msdn.microsoft.com/Forums/en/wpf/thread/580234cb-e870-4af1-9a91-3e3ba118c89c