解决方法

在你的表单代码</form>上方添加一行
{$field.hidden}

完整demo

{eyou:guestbookform type='default' typeid='132'}
	<form action="{$field.action}" method="post" enctype="multipart/form-data">
		<span>留言</span>
		<input type="text" placeholder="姓名" id='attr_60' name='{$field.attr_60}'/>
		<input type="text" placeholder="邮箱" id='attr_63' name='{$field.attr_63}' required />
		<input class="submit" type="submit" value="提交"/>
		{$field.hidden}
	</form>
{/eyou:guestbookform}