试试这个

<?php $model=new Upload(); ?>

<?php if(isset($_POST['Upload'])){$model->attributes=$_POST['Upload'];

$this->file=CUploadedFile::getInstance($model,'file');

}?>

<?php echo CHtml::link('Download file',array('/upload/download','id'=>$this->file->getName())); ?>

此处为文档https://www.yiiframework.com/doc/api/1.1/CUploadedFile

我重写了我的代码如下：
我的模型：

<?php

class Upload extends CFormModel
{
    public $file;
    public function rules()
    {
        return array(
                array('file', 'file', 'types'=>'pdf'),
        );
    }

    public function downloadFile($fullpath){
        $dir = Yii::getPathOfAlias('application.uploads');
        $filename= $fullpath;

        if(!empty($fullpath)){
            $file = $dir."\\"."$filename";

            header("Content-type: application/pdf");
            header("Content-Disposition: inline; filename=$filename");
            @readfile($file);

            Yii::app()->end();
        }
        else {return false;}

    }
}

我的控制器：

<?php

class UploadController extends Controller
{
     public  $file;

    function actionIndex()
    {
        $dir = Yii::getPathOfAlias('application.uploads');

        $uploaded = false;
        $model=new Upload();

        if(isset($_POST['Upload']))
        {
            $model->attributes=$_POST['Upload'];

            $this->file=CUploadedFile::getInstance($model,'file');

            $file=$this->file;

            if($model->validate()){
                $uploaded = $file->saveAs($dir.'/'.$file->getName());

            }
        }
        $this->render('index', array(
                'model' => $model,
                'uploaded' => $uploaded,
                'dir' => $dir,
        ));
    }

    public function actionDownload($id){

        $path = Yii::getPathOfAlias('/yiiroot/trackstar/protected/uploads/')."$id";

        $upload=new Upload();

        $upload->downloadFile($path);
    }
}

我的看法：

<?php if($uploaded):?>

<p>File was uploaded. Check <?php echo $dir?>.</p>

<?php endif ?>
<?php echo CHtml::beginForm('','post',array
('enctype'=>'multipart/form-data'))?>
<?php echo CHtml::error($model, 'file')?>
<?php echo CHtml::activeFileField($model, 'file')?>
<?php echo CHtml::submitButton('Upload')?>
<?php echo CHtml::endForm()?>
<br/>

<?php $model=new Upload(); ?>

<?php if(isset($_POST['Upload'])){$model->attributes=$_POST['Upload'];

$this->file=CUploadedFile::getInstance($model,'file');

echo CHtml::link('Download file',array('/upload/download','id'=>$this->file->getName())); 

}?>

请参阅：PHP getName() Function