I got the answer. We may not do configuration from web interface, there's no entry. But you can change the code in web_analytics module. Here's how: go to web_analytics/static/src/js/web_analytics.js , change the content. ($sudo nano web_analytics/static/src/js/web_analytics.js) find this paragraph:

init: function(webclient) {
          list item
          var self = this;
           self.initialized = $.Deferred();
           _gaq.push(['_setAccount', **'UA-xxxxxxxx-x**']);
           _gaq.push(['_setDomainName', '**.openerp.com**']);  // Allow    multi-domain
           self.initialize_custom(webclient).then(function()    {
               webclient.on('state_pushed', self,    self.on_state_pushed);
               self.include_tracker();
           });

just change the account and domain name, then install web_analytics module in your database. you would find there're some tracking infor (like which page/screen is viewed. whick module is working...) then through google analytics.

you can set Google Analytics Key directly from

Settings > Configurations > Website Settings view