Uncheck All Checkbox on Page Load for Apex Page Using Javascript

1. Put the following javascript function at "Function and Global Variable Declaration" of page attributes.

 function UncheckAll(){ 
      var w = document.getElementsByTagName('input'); 
      for(var i = 0; i < w.length; i++){ 
        if(w[i].type=='checkbox'){ 
          w[i].checked = false; 
        }
      }
  } 

2. Create page dynamics

  Event: Page Load
  Condition: No Condition
  Action: Eecute Javascript Code
  Code: UncheckAll()
  

Locate and open the true event "Execute Javascript Code" of create dynamic action, check "Fire On Page Load"