Loading subdomain post in main domain?

You can load wp-load.php to display posts.

Look at these links that will help you:

link

One option is you use RSS Feed Wordpress works with some plugins that might be interesting, at a glance at wordpress.org/plugins/tags/rss-feed

It's just a question of using switch_to_blog() and switch to the blog you want, make a query blog posts and use the same function to switch back to the original blog.

Create a Must plugin (always active and available at the entire network) and put the following code:

if( !function_exists('get_blog_posts') )
{
    function get_blog_posts( $blog_id, $args = array() )
    {
        $current_blog_id = get_current_blog_id();
        switch_to_blog( $blog_id );

        $posts = get_posts( $args );
        switch_to_blog( $current_blog_id ); // get_posts já foi feito, podemos restaurar

        if( $posts )
            return $posts;

        return false;
    }
}

Then in the template of the theme or in some function within functions.php , use the following, setting $blog_id_consultar and $parametros . Note that echo print_r() is for verification only, loop $posts_do_blog to print HTML:

<?php 
if( function_exists('get_blog_posts') ) { 
    $blog_id_consultar = '3';
    $parametros = array(); // VIDE http://codex.wordpress.org/Function_Reference/get_posts
    $posts_do_blog = get_blog_posts( $blog_id_consultar, $parametros );
    if( $posts_do_blog ) {
        echo '<pre>' . print_r( $posts_do_blog, true ) . '</pre>';
    }
}
?>

<?php
query_posts('showposts=4'); //Query WordPress para listar os últimos 4 posts
?>
<?php while (have_posts ()): the_post(); ?>
    <h2>
        <a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
    </h2>
    <p><?php the_author(); ?> | <?php the_date(); ?>
<?php the_post_thumbnail('thumbnail', array('class' => 'alignleft')); ?>
    <?php the_excerpt(); ?>
<?php endwhile; ?>

I'm using this code, I want it to load posts from another WordPress blog.