<TextBox x:Name="txtPlaceHolder1"
Padding="30,0,30,0" Text="" Width="468" FontSize="32" Height="72"
HorizontalAlignment="Center" VerticalAlignment="Center" VerticalContentAlignment="Center" >
HorizontalAlignment="Center" VerticalAlignment="Center" VerticalContentAlignment="Center" >
</TextBox>
在textbox控件中加入 Padding 属性 , Paddin的四个值分别表示距离textbox边框的距离 左,上,右,下;之后根据需求修改值的大小即可