for (int i = 0; i < niList.Count; i++)
            {  
                NeFtpInfo neIn = niList[i];
                DownLoadOneServer dlone = new DownLoadOneServer(neIn);
                Thread throne = new Thread(dlone.toDownLoadOne); //注意这块是函数名，不加"()",而不是函数调用
                throne.Start();
            }

            Class Object = new Class();
            Thread th = new Thread(Object.Method);
             th.start();

using System;
using System.Collections.Generic;
using System.Text;

namespace FTPDownLoad
{
    class DownLoadOneServer
    {
        NeFtpInfo nfi = new NeFtpInfo();
        public DownLoadOneServer(NeFtpInfo nfi)
        {
            this.nfi = nfi;
        }
        public void toDownLoadOne()
        {
            FtpHelper ftphelper = new FtpHelper(nfi.ServerIP, nfi.UserName, nfi.Password);
            ftphelper.DownLoadDirectory(nfi.ServerPath, nfi.LocalPath);
        }
    }
}