$items = array( 
  1 => array('id' => 1, 'pid' => 0, 'name' => '江西省'), 
  2 => array('id' => 2, 'pid' => 0, 'name' => '黑龍江省'),
  3 => array('id' => 3, 'pid' => 1, 'name' => '南昌市'), 
  4 => array('id' => 4, 'pid' => 2, 'name' => '哈爾濱市'),
  5 => array('id' => 5, 'pid' => 2, 'name' => '雞西市'), 
  6 => array('id' => 6, 'pid' => 4, 'name' => '香坊區(qū)'), 
  7 => array('id' => 7, 'pid' => 4, 'name' => '南崗區(qū)'), 
  8 => array('id' => 8, 'pid' => 6, 'name' => '和興路'), 
  9 => array('id' => 9, 'pid' => 7, 'name' => '西大直街'), 
  10 => array('id' => 10, 'pid' => 8, 'name' => '東北林業(yè)大學'),
  11 => array('id' => 11, 'pid' => 9, 'name' => '哈爾濱工業(yè)大學'),
  12 => array('id' => 12, 'pid' => 8, 'name' => '哈爾濱師范大學'),
  13 => array('id' => 13, 'pid' => 1, 'name' => '贛州市'), 
  14 => array('id' => 14, 'pid' => 13, 'name' => '贛縣'), 
  15 => array('id' => 15, 'pid' => 13, 'name' => '于都縣'), 
  16 => array('id' => 16, 'pid' => 14, 'name' => '茅店鎮(zhèn)'), 
  17 => array('id' => 17, 'pid' => 14, 'name' => '大田鄉(xiāng)'), 
  18 => array('id' => 18, 'pid' => 16, 'name' => '義源村'), 
  19 => array('id' => 19, 'pid' => 16, 'name' => '上壩村'), 
  20 => array('id' => 20, 'pid' => 0, 'name' => '廣東省'), 
  21 => array('id' => 21, 'pid' => 20, 'name' => '廣州市'),
); 
$t = array(); 
foreach ($items as $id => $item) { 
  if ($item['pid']) { 
    $items[$item['pid']][$item['id']] = &$items[$item['id']];
    $t[] = $id; 
  } 
} 
foreach($t as $u) { 
  unset($items[$u]); 
} 
echo "<pre>"; 
print_r($items);