<?php 
namespace frontend\controllers;
use Yii;
use yii\web\Controller;
use frontend\models\Uploadm;
use yii\web\UploadedFile;
class FormController extends Controller{
  public function actionMyfiles(){
      $model=new Uploadm();
      return $this->renderPartial('myfiles',['model'=>$model]);
  }
  public function actionGetfiles(){
    $model = new Uploadm();
    if (Yii::$app->request->isPost) {
      $model->imgFile = UploadedFile::getInstances($model, 'imgFile');
      if ($model->upload()) {
        // 文件上傳成功
        echo '上傳成功';
      }
    }
  }

<?php
namespace frontend\models;
use Yii;
use yii\base\Model;
use yii\web\UploadedFile;
class Uploadm extends Model
{
  public $imgFile;
  public function rules(){
    return [
       [['imgFile'], 'file','maxFiles' => 5],//最多5張
    ];
  }
  public function upload()
  {
   if ($this->validate()) { 
     foreach ($this->imgFile as $file) {
       $file->saveAs('uploads/' . $file->baseName . '.' . $file->extension);
     }
     return true;
   } else {
     return false;
   }
  }
} 

<?php
use yii\helpers\Html;
use yii\widgets\ActiveForm;
$form = ActiveForm::begin([
  'id' => 'login-form',
  'options' => ['class' => 'form-horizontal','enctype' => 'multipart/form-data'],
  'action'=>'?r=form/getfiles',
  'method'=>'post'
]) ?>
  <?= $form->field($model, 'imgFile[]')->fileInput(['multiple' => true]) ?>

  <div class="form-group">
    <div class="col-lg-offset-1 col-lg-11">
      <?= Html::submitButton('上傳', ['class' => 'btn btn-primary']) ?>
    </div>
  </div>
<?php ActiveForm::end() ?>