<?php
					$current_category=get_the_category();
					$prev_post = get_previous_post($current_category,'');
					$next_post = get_next_post($current_category,'');
				?>
				<p class="previous_post_link fl">
					<?php if (!empty( $prev_post )): ?>
						<a href="<?php echo get_permalink( $prev_post->ID ); ?>"><?php echo get_the_post_thumbnail( $prev_post->ID, '', '' ); ?></a>
						上一篇: <a href="<?php echo get_permalink( $prev_post->ID ); ?>"><?php echo $prev_post->post_title; ?></a>
					<?php endif; ?>
				</p>
				<p class="next_post_link fr">
					<?php if (!empty( $next_post )): ?>
						<a href="<?php echo get_permalink( $next_post->ID ); ?>"><?php echo get_the_post_thumbnail( $next_post->ID, '', '' ); ?></a>
						上一篇: <a href="<?php echo get_permalink( $next_post->ID ); ?>"><?php echo $next_post->post_title; ?></a>
					<?php endif; ?>
				</p>

好人做到底.
自己看着修改吧.

function nav_link_with_thumb(){
         $output = '';
         $prev_post = get_previous_post();
         if ($prev_post){
         	 $output .= get_the_post_thumbnail($prev_post->ID, 'thumbnail');
             $prev_post->filter='sample';
             $output .= 'Previous Post: <a href="'.get_permalink( $prev_post ).'">'.$prev_post->post_title.'</a>';
         }
         $next_post = get_next_post();
         if ($next_post){
             $output .= get_the_post_thumbnail($next_post->ID, 'thumbnail');
             $next_post->filter='sample';
             $output .= 'Next post: <a href="'.get_permalink( $next_post ).'">'.$next_post->post_title.'</a>';
         }
         echo $output;
}

能支持下tab吗?