1. URL 美化设置, http://yinzhezq.blog.163.com/blog/static/164862890201581984113653
 'urlManager' => [
            'enablePrettyUrl' => true,
            'showScriptName' => false,
        ],

2. 开启gii功能
    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = [ 
        'class' => 'yii\gii\Module',
        'allowedIPs' => ['127.0.0.1', '::1', '192.168.0.*', '设置你浏览器主机的IP'],
    ];  

3. 访问地址： http://XXX/gii                      
   XXX表示访问首页的地址

4. 原因：当启动gii模块的时候，会自动设置gii的美化URL访问规则
vendor/yiisoft/yii2-gii/Module.php

    /** 
     * @inheritdoc
     */
    public function bootstrap($app)
    {   
        if ($app instanceof \yii\web\Application) {
            $app->getUrlManager()->addRules([
                $this->id => $this->id . '/default/index',
                $this->id . '/<id:\w+>' => $this->id . '/default/view',
                $this->id . '/<controller:[\w\-]+>/<action:[\w\-]+>' => $this->id . '/<controller>/<action>',
            ], false);
        } elseif ($app instanceof \yii\console\Application) {
            $app->controllerMap[$this->id] = [ 
                'class' => 'yii\gii\console\GenerateController',
                'generators' => array_merge($this->coreGenerators(), $this->generators),
                'module' => $this,
            ];  
        }   
    }   

'<controller:\w+>/<name:\w+>/<action:\w+>'=>'<controller>/<action>'

关于美化url见，http://yinzhezq.blog.163.com/blog/static/164862890201581984113653/