<?php 
echo Html::a('添加请假单', ['create'], ['class' => 'btn btn-success','data-toggle'=>'modal','data-target'=>'#ajax']) 
?>

<div class="modal bs-example-modal-lg" id="ajax">

 <div class="modal-dialog">
 
 <div class="modal-content width_reset" id="tmpl-modal-output-render"> </div>
 
 </div>

</div>

   return $this->renderAjax('create', [
    'model' => $model,
   ]); 
   

<?php $form = ActiveForm::begin(['options' => ['enctype' => 'multipart/form-data'],'id'=>'leave-form-self']) ?>
指向 你的models 在rules添加上验证规则

 public function rules()
 {
  return [
   [['t_leave_date', 't_days', 't_reason', 't_nickname','t_leave_enddate'], 'required'],
   [['t_leave_date', 't_leave_enddate'], 'safe'],
   [['t_days'], 'number'],
   [['t_reason'], 'string'],
   [['type', 'add_time', 'uid', 'update_time', 'status', 'is_shen'], 'integer'],
   [['t_pickup', 't_nickname', 't_pass'], 'string', 'max' => 20],
   [['t_img', 'reviewer_user', 'audit_user'], 'string', 'max' => 255]
  ];
 }