没关系，我已经找到了答案。

在Site.Master.cs添加此行：

 使用Microsoft.AspNet.Identity;
使用Microsoft.AspNet.Identity.Owin;
使用Owin;
使用EvSiProject.Models;
使用Microsoft.AspNet.Identity.EntityFramework;
 

然后添加此行对在Page_Load（）函数：

 如果（Context.User.Identity.IsAuthenticated）
    {
        VAR经理=新的UserManager＆LT; ApplicationUser＆GT;（新UserStore＆LT; ApplicationUser＆GT;（新ApplicationDbContext（）））;
        变种的cu​​rrentUser = manager.FindById（Context.User.Identity.GetUserId（））;        //字符串FNAME = currentUser.FirstName;
        //字符串LNAME = currentUser.LastName;
    }
 

这就是它。

How can I access custom user properties(eg. first name, last name) on the master page if the Web Forms Project is using Asp.Net Identity System? I've already made this configurations http://www.itorian.com/2013/11/customize-users-profile-in-aspnet.html but my project is not MVC is Web Forms.

By default I can only access user's name using:

Context.User.Identity.GetUserName()

Never mind, I've found the answer.

On Site.Master.cs add this lines:

using Microsoft.AspNet.Identity;
using Microsoft.AspNet.Identity.Owin;
using Owin;
using EvSiProject.Models;
using Microsoft.AspNet.Identity.EntityFramework;

Then add this lines on the Page_Load() function:

    if (Context.User.Identity.IsAuthenticated)
    {
        var manager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));
        var currentUser = manager.FindById(Context.User.Identity.GetUserId());

        //string fName = currentUser.FirstName;
        //string lName = currentUser.LastName;
    }

And that's it.