Now i am deploying from Dev to QA server. 

Although the deploying has finished to QA but the   "Generating mobile apps" hasn't finished.

the status has been continuing more than 3 hours.

i checked the latest version in QA  and it definitely completed deployment.

How can i  cancel or complete this ?

I solved this by doing  the below.

  1. Write down the Staging ID of the staging that wasn't successfully completed;
  2. How to get the Staging ID? Go to Lifetime > Applications > Click in target environment name > Change Log > Check for "Created deployment plan #<NUMBER> between environments 'X' and 'Y').
  3. Access to http://<yourinfrastructure>/lifetime/ForceStagingClose.aspx and introduce the Staging ID that you want to abort.