How to realize login manager with ICE?

Hi!
I am a beginner to use ICE, i feel ICE is a powerful tool, it make my work
easy, but i dont know how to control my clients , some clients only query data ,some clients can modify data ...
in the server, how can i control clients , i need how much clients have connected, i need close some client's connection;

You can implement a session manager with Glacier, and you can also give different clients different permissions with Glacier. Have a look at the chapter about Glacier in the manual, and at the demo in demo/Glacier/session.

reading document......

I study the document , my system's clients and server in one local NET ,if i use Glacier's session manager , my system will be forced add
a layer, if servant have some ability that manage connected clients ,my system dont need to use Glacier .

There are many ways to handle a login manager and sessions. An exhaustive discussion of this topic could easily fill a chapter in a book (which we perhaps have to write some day ), so I'm afraid I need to know more details about what exactly your requirements are, otherwise it's difficult for me to give advice.

requirement: Server count the connected clients,and when the clients connected and disconnected ,server handle this events and report it.
How can server handle client's connect and disconnection events,

It cannot. There is no concept of connections at the user level of Ice. Furthermore, there is no direct relationship between connections and clients. A client can open several connections to a server, and connections may be closed and reopened transparently by both clients and servers.