How to copy select list value from a webform submisison into select list field new node?
Well, finally i figure it out how to solve it.

I'm using Webform Rules module

Just need to add an Execute custom PHP code action and set the value like this

// $new_question is my new node.
// $data['components']['category'] is my webform listbox component.
// $new_question-&gt;field_category is my taxonomy reference field select list.

$tid = substr($data['components']['category']['value'][0],4,2);
$new_question-&gt;field_category['und'][0]['tid'] = $tid;