<div class="mian_block">
  <div class="hide">r</div>
  <div class="content_block">
  <a>CFDE</a>
  
</div>
  
  
</div>

.mian_block{
  background:red;
  margin:8px;
  padding:6px;
}

.content_block{
  background:green;
  margin:8px;
  padding:6px;
}

.content_block a{
  background:blue;
  margin:8px;
  padding:6px;
}
.hide{
    background:yellow;
  margin:8px;
  padding:6px;
}

$( "body" ).on('mousedown', '.mian_block', function(e) {
  if(! $(e.target).hasClass("content_block")){
    alert('f');
  }
    
  })