您需要创建具有提升权限的新对象.

You need to create new object with elevated privieges.

SPSecurity.RunWithElevatedPrivileges(delegate()
{
    SPSite oSite = new SPSite(SPContext.Current.Site.ID); 
    SPWeb oWeb = oSite.OpenWeb(SPContext.Current.Web.ID);                                 
    demoList = oWeb.Lists["nameList"];
});

另外，你应该处理新创建的对象，不需要两个委托.

Also, you should dispose of the newly created objects and there is no need for two delegates.

SPSecurity.RunWithElevatedPrivileges(delegate {
    using (SPSite oSite =new SPSite(SPContext.Current.Site.ID))
    using (SPWeb oWeb = oSite.OpenWeb()) {
        var demoList = oWeb.Lists["nameList"];
        SPQuery oQuery = new SPQuery
                            { Query = "<OrderBy><FieldRef Name='Date' Ascending='False' /></OrderBy>" };
        SPListItemCollection collListItems = demoList.GetItems(oQuery);

        //IF ADMIN
        //collListItems.Count ==>3

        //IF NO ADMIN 
        //collListItems.Count ==>0
    }
});