你的方法是正确的。如果您发布代码，效果会更好，但类似这样：

$args = array(
    \'post_type\' => \'project\',
    \'tax_query\' => array(
        array(
            \'taxonomy\' => \'region\',
            \'field\'    => \'slug\',
            \'terms\'    => $region, //set your region
        ),
    ),
);
$the_query = new WP_Query( $args );

// The Loop of Projects by Region
if ( $the_query->have_posts() ) {

    $projectsid = array();
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        $projectsid[] = get_the_ID();
    }

    $args = array(
        \'post_type\' => \'unit\',
        \'meta_query\' => array(
            array(
                \'key\'       => $keyname, //set the key name which store ID
                \'value\'     => $projectsid,
                \'compare\'   => \'IN\',
                \'type\'      => \'NUMERIC\'
            ),
        ),
    );
    $the_query = new WP_Query( $args );

    // The Loop of units in project per region
    if ( $the_query->have_posts() ) {

        while ( $the_query->have_posts() ) {
            $the_query->the_post();
            //do something

        }

    } else {

        //No units for projects in this region

    }

} else {

    //No projects in this region

}

wp_reset_query();