using(StreamReader sr=new StreamReader(@"c:\1.txt",Encoding.Unicode)){
    textBox1.Text=sr.ReadToEnd();
}

弱弱的问楼上：我说的是在VB.NET里面，楼上的写的是C吧？

using(StreamReader sr=new StreamReader(@"c:\1.txt",Encoding.Unicode)){
    textBox1.Text=sr.ReadToEnd();
}.ConvertToVBdotnet() ==
Dim sr As New StreamReader("c:\1.txt", Encoding.Unicode)
TextBox1.Text = sr.ReadToEnd()

注意需要Imports System.IO