category__and 是独占的，因此如果您使用tax_query 并按如下方式设置查询，它应该可以工作：

$args = array(
    \'tax_query\' => array(
        \'relation\' => \'AND\',
        array(
            \'taxonomy\' => \'category\',
            \'field\'    => \'id\',
            \'terms\'    => $city,
            //\'include_children\' is true by default
        ),
        array(
            \'taxonomy\' => \'category\', //may need to be categories, I don\'t recall, tweak it till it works.
            \'field\'    => \'id\',
            \'terms\'    => $category,
            //\'include_children\', again, is true by default
        )
    )
);
$posts = query_posts( $args );