分类category是在你修改固定链接格式后才出现的。陌小雨在测试的时候发现会出现404页面，经过摸索，顺利解决，现分享如下：
后台→设置→固定链接，先更改为其他的，再更改回来/%post_id%.html，清空下浏览器缓存。陌小雨用的是这个。
代码如下：

/* 
 * no category
 * ====================================================
*/
// if( function_exists('no_category_base_refresh_rules') ) return;

register_activation_hook(__FILE__, 'no_category_base_refresh_rules');
add_action('created_category', 'no_category_base_refresh_rules');
add_action('edited_category', 'no_category_base_refresh_rules');
add_action('delete_category', 'no_category_base_refresh_rules');
function no_category_base_refresh_rules() {
    global $wp_rewrite;
    $wp_rewrite -> flush_rules();
}

register_deactivation_hook(__FILE__, 'no_category_base_deactivate');
function no_category_base_deactivate() {
    remove_filter('category_rewrite_rules', 'no_category_base_rewrite_rules');
    // We don't want to insert our custom rules again
    no_category_base_refresh_rules();
}

// Remove category base
add_action('init', 'no_category_base_permastruct');
function no_category_base_permastruct() {
    global $wp_rewrite, $wp_version;
    if (version_compare($wp_version, '3.4', '<')) {
        // For pre-3.4 support
        $wp_rewrite -> extra_permastructs['category'][0] = '%category%';
    } else {
        $wp_rewrite -> extra_permastructs['category']['struct'] = '%category%';
    }
}

// Add our custom category rewrite rules
add_filter('category_rewrite_rules', 'no_category_base_rewrite_rules');
function no_category_base_rewrite_rules($category_rewrite) {
    //var_dump($category_rewrite); // For Debugging

    $category_rewrite = array();
    $categories = get_categories(array('hide_empty' => false));
    foreach ($categories as $category) {
        $category_nicename = $category -> slug;
        if ($category -> parent == $category -> cat_ID)// recursive recursion
            $category -> parent = 0;
        elseif ($category -> parent != 0)
            $category_nicename = get_category_parents($category -> parent, false, '/', true) . $category_nicename;
        $category_rewrite['(' . $category_nicename . ')/(?:feed/)?(feed|rdf|rss|rss2|atom)/?$'] = 'index.php?category_name=$matches[1]&feed=$matches[2]';
        $category_rewrite['(' . $category_nicename . ')/page/?([0-9]{1,})/?$'] = 'index.php?category_name=$matches[1]&paged=$matches[2]';
        $category_rewrite['(' . $category_nicename . ')/?$'] = 'index.php?category_name=$matches[1]';
    }
    // Redirect support from Old Category Base
    global $wp_rewrite;
    $old_category_base = get_option('category_base') ? get_option('category_base') : 'category';
    $old_category_base = trim($old_category_base, '/');
    $category_rewrite[$old_category_base . '/(.*)$'] = 'index.php?category_redirect=$matches[1]';

    //var_dump($category_rewrite); // For Debugging
    return $category_rewrite;
}

// For Debugging
//add_filter('rewrite_rules_array', 'no_category_base_rewrite_rules_array');
//function no_category_base_rewrite_rules_array($category_rewrite) {
//  var_dump($category_rewrite); // For Debugging
//}

// Add 'category_redirect' query variable
add_filter('query_vars', 'no_category_base_query_vars');
function no_category_base_query_vars($public_query_vars) {
    $public_query_vars[] = 'category_redirect';
    return $public_query_vars;
}

// Redirect if 'category_redirect' is set
add_filter('request', 'no_category_base_request');
function no_category_base_request($query_vars) {
    //print_r($query_vars); // For Debugging
    if (isset($query_vars['category_redirect'])) {
        $catlink = trailingslashit(get_option('home')) . user_trailingslashit($query_vars['category_redirect'], 'category');
        status_header(301);
        header("Location: $catlink");
        exit();
    }
    return $query_vars;
}

使用方法：将上述代码放到主题functions.php就可以了。