php curl发送帖子数据问题

I'm trying to get the data of a page by curl library. I can do it with simple link, but when I'm going to submit a form and then get the data , I can not. It returns me the default value of page, not the submitted form. Let me explain the code.

$url = ...
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POST, 1);
// I'm sending post data
$params = array(
      'madrak'=>5,
      'B1' => 'مشاهده اطلاعات'
);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
// and execute...

The page I'm getting data is written with asp and the form part of that page is this:

<input type="submit" value="مشاهده اطلاعات" name="B1">

<select name="madrak" size="1" class="style1" id="1">
  <option value="1">زير ديپلم</option>
  <option value="5">ديپلم</option>
  <option value="6">فوق ديپلم</option>
  <option value="7">ليسانس</option>
  <option value="8">فوق ليسانس</option>
  <option value="9">دكترا</option>
  <option selected="" value="6">فوق ديپلم</option>
 </select>

It seems that the form is not being submitted. Because just I can get the data which is loading without form submitting. Any idea?

First I should mention that you don't have to build query string of the post data. You can pass the array.

Please try setting HTTP Headers too. Like content type, user agents and etc, the target website might check for the headers.

But the most important part is to set Content-Type: application/x-www-form-urlencoded HTTP Header.

curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/x-www-form-urlencoded']);