When I click a radio button its value should display in textfield
You should use drupal ajax form 
 try this code

function test_radio_form($form, &amp;$form_submit){

/* the options to display in our form radio buttons */
$options = array(
  'one' =&gt; t('One'),
   'two' =&gt; t('Two'),
);

$form['count'] = array(
  '#title' =&gt; t('Count'),
  '#type' =&gt; 'radios',
  '#options' =&gt; $options,
  '#ajax' =&gt; array(
            'callback' =&gt; 'myid_print_all_submitted_id_callback',
            'wrapper' =&gt; 'myid_print_search_idnumber_wrapper',
  ),

);

$form['display'] = array(
'#title' =&gt; t('Display'),
'#type' =&gt; 'textfield',
'#value' =&gt; isset($form_state['values']['count']) ? $form_state['values']['count'] : '',
'#prefix' =&gt; '&lt;div id="myid_print_search_idnumber_wrapper"&gt;',
'#suffix' =&gt; '&lt;/div&gt;',
  );

$form['submit'] = array(
'#value' =&gt; t('PROCEED'),
'#type' =&gt; 'submit',
  );

return $form;
}
function myid_print_all_submitted_id_callback($form, $form_state)
{
      return $form['display'];
}