Cancel a timer job

when you register a timer job, it creates a timer job definition. as long as timer job definition stays in, Sharepoint will kick off the job based on its definition which is for example every 5 minute or once in a day etc. So if your requirement is to cancel a job, you will need to delete the timer job definition. However if timer job has started executing, you can not really STOP it unless you reset IIS or stop Sharepoint Windows Timer Service. so programmatically you can control the cancellation of a job in advance before that scheduled time reaches but you can not really control the other thing which is to stop an executing job. and restarting WSS timer service is not a good idea to acheive the second part.

Source : Internet