how to create a multi select box with out selected options codeigniter

You should use the form_multiselect() helper.

$options = array(
                  'small'  => 'Small Shirt',
                  'med'    => 'Medium Shirt',
                  'large'   => 'Large Shirt',
                  'xlarge' => 'Extra Large Shirt',
                );

echo form_multiselect('shirts', $options);