db = mysqli_connect("localhost", "test", "123456", "test_t");
$zh = $_POST[lbk]'zh'[rbk];
$mm = $_POST[lbk]'mm'[rbk];
$mm1 = $_POST[lbk]'mm1'[rbk]; $sqlxm = mysqli_query($db, "SELECT * FROM admin1 WHERE admin = '$zh'");
$sqlsz = mysqli_fetch_array($sqlxm);
if ($zh != $sqlsz[lbk]'admin'[rbk]) { if ($mm == $mm1) { mysqli_query($db,"insert into admin1 (admin,password) values ('$zh', '$mm') "); header("location: login.html"); exit; }
else { echo "1"; exit; }

挨个排除.
把每个值打印出来看看.

admin是数据表的字段吧