它不存在，但是您可以从Dictionary and List快速构建一个：

class MultiDict<TKey, TValue>  // no (collection) base class
{
   private Dictionary<TKey, List<TValue>> _data =  new Dictionary<TKey,List<TValue>>();

   public void Add(TKey k, TValue v)
   {
      // can be a optimized a little with TryGetValue, this is for clarity
      if (_data.ContainsKey(k))
         _data[k].Add(v)
      else
        _data.Add(k, new List<TValue>() { v}) ;
   }

   // more members
}