方法一

var isA = oldObject.GetType() == typeof(Dictionary<string, string>)；

方法二

var isB = oldObject.GetType().FullName.IndexOf("Dictionary") > 0;

方法三

var isC = oldObject is Dictionary<string, string>;

参考：
https://www.cnblogs.com/luyj00436/p/14833883.html