可以类似这样处理。
main-local.php:

'components' => [
        'db' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=192.168.80.1;dbname=test1;port=3306',
            'username' => 'root',
            'password' => '123456',
            'charset' => 'utf8',
        ],
		'db2' => [
			'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=192.168.80.1;dbname=test2;port=3306',
            'username' => 'root',
            'password' => '123456',
            'charset' => 'utf8',
		],

Model:

$connection = \Yii::$app->get ( "db" );
或
$connection = \Yii::$app->get ( "db2" );

@ftdxl 在对应表的model里设置你要使用哪个库