方法一：

         Private   Sub   TextBox1_KeyPress(ByVal   sender   As   Object,   ByVal   e   As   System.Windows.Forms.KeyPressEventArgs)   Handles   TextBox1.KeyPress   
                 Dim strlimit As String
                 strlimit = "0123456789."
                 Dim keychar As Char = e.KeyChar
                 If InStr(strlimit, keychar) <> 0 Or e.KeyChar = Microsoft.VisualBasic.ChrW(8) Then
                              If keychar = "." And InStr(TxtEnter.Text, keychar) <> 0 Then
                                  e.Handled = True
                              Else
                                  e.Handled = False
                              End If
                 Else
                              e.Handled = True
                 End If
          End   Sub  

方法二：
IsNumeric(TextBox1.Text)

方法三：
    Private Sub TextBox1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyUp
        If (e.KeyValue > 47 And e.KeyValue < 58) Or (e.KeyValue > 95 And e.KeyValue < 106) Or (e.KeyValue = 8) Or (e.KeyValue = 45) Or (e.KeyValue = 46) Then
            str = TextBox1.Text
        Else
            TextBox1.Text = str
            TextBox1.Focus()
        End If
    End Sub

方法四：
文本框防止非法字符輸入：
只輸入整數(shù)：
Private Sub Text1_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case Asc("0") To Asc("9"), vbKeyBack
'nop
Case Else
KeyAscii = 0
End Select
End Sub
只輸入小數(shù):
Private Sub Text1_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case Asc("0") To Asc("9"), vbKeyBack
'nop
case Asc(".")'允許一個小數(shù)點
If InStr(1, Text1.Text, ".") > 0 Then KeyAscii = 0
Case Else
KeyAscii = 0
End Select
End Sub