I want to add relationship (civicrm) at the time of creation of new user using drupal user. (individual -> Household).
You could create a Drupal rule to achieve this provided you have that functionality turned on.
Could use the 'Civicrm contact has been created' event.
Checkout the Drupal 7 rules module: https://www.drupal.org/project/rules Civicrm comes with Civicrm rule intergration module which you can enabled (although you may not need to enable this).