I have find the solution of it!
here is the code for share~
function my_acf_save_post( $post_id ) {
$args = array(
'post_type' => 'point'
);
$opt_array = array();
$the_query = new WP_Query($args);
while ($the_query -> have_posts()): $the_query -> the_post();
array_push($opt_array, array(
'point_location' => get_field('point_location')
)
);
endwhile;
wp_reset_postdata();
file_put_contents($_SERVER['DOCUMENT_ROOT'] . '/wp-content/themes/test2/json/data.json', json_encode($opt_array));
}
add_action('acf/save_post', 'my_acf_save_post', 10, 2);