I downloaded CEF (chromuim embedded framework) binary distributation that comes with (cefclient & cefsimple) c++ examples, And Realized that cefclient can change proxy s
if anyone need any other soulition i found this solution.
Cef.UIThreadTaskFactory.StartNew(delegate
{
string ip = "ip or adress";
string port = "port";
var rc = this.browser.GetBrowser().GetHost().RequestContext;
var dict = new Dictionary();
dict.Add("mode", "fixed_servers");
dict.Add("server", "" + ip + ":" + port + "");
string error;
bool success = rc.SetPreference("proxy", dict, out error);
});