mac hard disk encrypted

I accidentally started the encrypt hard disk within security setting of my macbook pro and could not kill the job as it said i have to wait for it to finish; however, it seemed to take forever and i had no clue wen it will finish or the action was frozen. How can I tell if it is still running or hanged, and once my hard disk is encrypted, how can I tell? Can I kill it in the middle?

Dear Pettycash, the answer to your question is, no you can't and indeed shouldn't stop the encryption process.
There have been a number of recent threads on this forum about accidental or unintended encryption of the HD by File Vault.
The amount of time it takes to encrypt is roughly equal to the time in takes to unencrypt which may be as much as 6 hrs or more depending on storage.
If it has already taken longer than that it may have encountered a problem. Check this article; Fix your Mac stuck on encrypting with FileVault | MacIssues
However if you get to the bit where it says, "Click the Unlock button, and then supply your FileVault password to unlock the drive." and you don't know what they are talking about then get back to this forum with the details of your MBP, Operating System, storage capacity etc. and we will try to help.

Thanks Rod, both your comment and the article are very helpful but now I am not so sure if I am having a slightly different issue: I get a full bar in the security screen indicating that the encryption is complete (?) but at the same time, the description beside the bar reads 'Encryption paused'. Further, when I tried to turn off encryption, there was a warning message that prompts me to wait until the disk is fully encrypted; thus, I don't know what the actual status is now...

Yes that is a separate problem in a way. You could try doing a search on this site for "File Vault Paused" or "encryption paused" I'm sure we have covered this topic because it has happened to quite a few OP.
Or I just found this but I have not tested it; http://www.iphonetopics.com/filevault-stuck-encryption-paused-fix-mac/

You will note there are similarities between both solutions; both require you to repair your Mackintosh HD. There seems no way around this. In either case you will need to boot from the recovery partition and "Unlock" the Mackintosh HD. I do so hope you have a password for this. In cases of accidental or unintended encryption I have found a little variation. One client successfully used their Admin password but encryption had already completed, another used their Apple ID.