假设这是WinForms
我认为您可以使用RichTextBox1.GetPositionFromCharIndex()和RichTextBox1.SelectionStart：

' Y pos of caret
Dim CaretYPos As Integer = RichTextBox1.GetPositionFromCharIndex(RichTextBox1.SelectionStart).Y
Dim CharHeight As Integer = 4 ' Height of each line

If CaretYPos >= RichTextBox1.Height - CharHeight Then
    ' Caret is hidden below screen view
ElseIf CaretYPos < -CharHeight Then
    ' Caret is hidden above screen view
Else
    ' Caret is visible
End If

不过，在使用CharHeight时，您可能需要考虑更高的dpi显示器

我将@jimi的注解应用到我的C#应用程序中，它与ScrollToCaret()方法配合使用效果很好。谢谢。

private void CheckAndMakeSelectionVisible()
{
    // other stuff
    if(!IsCaretVisible()) {
        richTextMsg.ScrollToCaret();
    }
}
private bool IsCaretVisible()
{
    if (!richTextMsg.ClientRectangle.Contains(richTextMsg.GetPositionFromCharIndex(richTextMsg.SelectionStart)))
    {
        // Outside visible bounds 
        return false;
    }
    else
        return true;
}