List<T> oldList = new List<T>();   
oldList.Add(..);   
List<T> newList = new List<T>(oldList); 

static class Extensions   
{   
    public static IList<T> Clone<T>(this IList<T> listToClone) where T: ICloneable   
    {   
        return listToClone.Select(item => (T)item.Clone()).ToList();   
    }   
    //<span style="color:#000000;">当然前题是List中的对象要实现ICloneable接口</span>  
}   

public static T Clone<T>(T RealObject)   
{   
    using (Stream objectStream = new MemoryStream())   
    {   
       //利用 System.Runtime.Serialization序列化与反序列化完成引用对象的复制  
        IFormatter formatter = new BinaryFormatter();   
        formatter.Serialize(objectStream, RealObject);   
        objectStream.Seek(0, SeekOrigin.Begin);   
        return (T)formatter.Deserialize(objectStream);   
    }   
}

public static T Clone<T>(T RealObject)   
{    
    using(Stream stream=new MemoryStream())  
    {  
        XmlSerializer serializer = new XmlSerializer(typeof(T));  
        serializer.Serialize(stream, RealObject);  
        stream.Seek(0, SeekOrigin.Begin);  
        return (T)serializer.Deserialize(stream);  
    }  
}

using System;  
using System.Collections.Generic;  
using System.Collections ;  
using System.Linq;  
using System.Text;  
using System.IO;  
using System.Runtime.Serialization;  
using System.Runtime.Serialization.Formatters.Binary;  

namespace LINQ  
{  
    [Serializable]  
    public class tt  
    {  
        private string name = "";  

        public string Name  
        {  
            get { return name; }  
            set { name = value; }  
        }  
        private string sex = "";  

        public string Sex  
        {  
            get { return sex; }  
            set { sex = value; }  
        }  
    }  

    class LINQTest  
    {  
        public static T Clone<T>(T RealObject)   
        {   
            using (Stream objectStream = new MemoryStream())   
            {   
                IFormatter formatter = new BinaryFormatter();   
                formatter.Serialize(objectStream, RealObject);   
                objectStream.Seek(0, SeekOrigin.Begin);   
                return (T)formatter.Deserialize(objectStream);   
            }   
        }  


        public static void Main()  
        {  
            List<tt> lsttt = new List<tt>();  
            tt tt1 = new tt();  
            tt1.Name = "a1";  
            tt1.Sex = "20";  
            lsttt.Add(tt1);  
            List<tt> l333 = new List<tt>();  
            l333.Add(Clone<tt>(lsttt[0]));  
            l333[0].Name = "333333333";  
      }  
   }  
}

ObservableCollection<T> tempList = new ObservableCollection<T>(sourceList);

sourceList.Clear(); // 清除源数据列表
System.Console.WriteLine(tempList.Count); // 副本数据并未改变