有三种方法可以做到这一点；您可以[XmlInclude]针对类型使用，也可以针对属性使用XmlElement/
XmlArrayItem。它们都显示在下面；取消注释您喜欢的那对：

using System;
using System.Collections.Generic;
using System.Xml.Serialization;
public class MyWrapper {
    //2: [XmlElement("A", Type = typeof(ChildA))]
    //2: [XmlElement("B", Type = typeof(ChildB))]
    //3: [XmlArrayItem("A", Type = typeof(ChildA))]
    //3: [XmlArrayItem("B", Type = typeof(ChildB))]
    public List<ChildClass> Data { get; set; }
}
//1: [XmlInclude(typeof(ChildA))]
//1: [XmlInclude(typeof(ChildB))]
public abstract class ChildClass {
    public string ChildProp { get; set; }
}
public class ChildA : ChildClass {
    public string AProp { get; set; }
}
public class ChildB : ChildClass {
    public string BProp { get; set; }
}
static class Program {
    static void Main() {
        var ser = new XmlSerializer(typeof(MyWrapper));
        var obj = new MyWrapper {
            Data = new List<ChildClass> {
                new ChildA { ChildProp = "abc", AProp = "def"},
                new ChildB { ChildProp = "ghi", BProp = "jkl"}}
        };
        ser.Serialize(Console.Out, obj);
    }
}