How can I stop Oracle Shutdown command? I used Shutdown normal, instead of Shutdown immediate. 

Now I want to stop the process, because its taking too long. 

How can I do it?
It seems like the obvious answer is that you can't stop a shutdown that is happening, but you can do either a shutdown immediate or shutdown abort from a different session if you did a shutdown normal. As long as you have enough online redo log groups and each group has a log that is large enough, then you can recover from either a shutdown immediate or shutdown abort. If you ask someone what is the exact risk that someone faces for doing a shutdown abort, they may struggle to answer you. On shutdown immediate transactions are rolled back as sessions are killed. On shutdown abort, all transactions are rolled back when the database is started up. Hence the same thing should be happening in both cases, just in a different order. Once you start a shutdown normal, either ask everyone to log out, or just do shutdown immediate in a different session. Either way, Oracle won't allow a database to open, if it isn't in a consistent state.