Drupal 7 Block View include File
There is no such an attribute in block_view function, but you can always use something like that (assuming that you have already implemented hook_block_info() and you have defined your own MYBLOCKDELTA):

function MYMODULENAME_block_view($delta = '') {
  switch ($delta) {
    case 'MYBLOCKDELTA':
      $block['subject'] = t('This is my block');
      module_load_include('inc', 'MYMODULENAME', 'my_inc_file');
      $block['content'] = myblock_contents($delta);
      break;
  }
  return $block;
}


Then define function myblock_contents($delta) in your my_inc_file.inc in MYMODULENAME module folder.