void Application_Start(object sender, EventArgs e) 
    {
        //在应用程序启动时运行的代码
        Framework.PlugsHostService.Instance.LoadPlugs();
    }

-------------

private bool alreadyLoad = false;

//查找所有的插件的路径
        private static List<string> FindPlugin()
        {
            List<string> PluginPaths = new List<string>();
            try
            {
                //获取当前程序的启动路径
                string path = appLocation;
                //合并路径,指向插件所在的目录
                path = Path.Combine(path, "Lib");
                string[] fileNames = Directory.GetFiles(path, "*.dll");
                foreach (string fileName in fileNames)
                {
                    PluginPaths.Add(fileName);
                }
            }
            catch (Exception exp)
            {
                throw exp;
            }


            return PluginPaths;
        }

public void LoadPlugs()
        {
            if (alreadyLoad)
            {
                return;
            }
            List<string> PluginPaths = FindPlugin();
            PluginPaths = DeleteInvalidPlugin(PluginPaths);
            foreach (string path in PluginPaths)
            {
                try
                {
                    //获得 文件名称 
                    string asmFile = path;
                    string asmName = System.IO.Path.GetFileNameWithoutExtension(asmFile);
                    if (asmFile != string.Empty)
                    {

                        // 利用反射,构造DLL文件的实例
                        System.Reflection.Assembly asm = System.Reflection.Assembly.LoadFile(asmFile);

                        Type[] t = asm.GetExportedTypes();
                        foreach (Type type in t)
                        {
                            if (type.GetInterface(typeof(IPlugs).FullName) != null)
                            {
                                IPlugs iPlugs = (IPlugs)System.Activator.CreateInstance(type);
                                // 在主程序中使用这个类的实例
                                //AppDomain.CurrentDomain.Load(asm.GetName());
                                //AppDomain.CurrentDomain.ExecuteAssembly(asmFile);//.ExecuteAssembly(asmFile);
                                AppDomain.CurrentDomain.Load(asm.FullName, AppDomain.CurrentDomain.Evidence); //调试时，到这里就报错
                            }
                        }
                    }
                    alreadyLoad = true;
                }
                catch (Exception ex)
                {
                    throw ex;
                }
            }
        }