I found a way well, it should look like this:
$selected = array(2, 3); $options = array(1, 2, 3, 4); echo $this->Form->input('Attendees', array('multiple' => true, 'options' => $options, 'selected' => $selected));
It will display:
The selected $ checks the key index of each item, not the value itself.
source share