What do you mean by "What happen if someone revise bitcoin source and launch it as like bitcoin"? That somebody may launch a "bitcoin wallet" on another website or through social media, and it's rigged to steal coins? Sure this can be done and has already happened, but it's just a matter of trusting the wallet and the page you got it from - it's just like a banking trojan, not really a danger for Bitcoin, just for people who are not careful about the software they use.
I thought if someone (has bad intent) revise bitcoin source and compile, and if he maintain 51% of total computing power, then he wins and his revised source take bitcoin name?
A 51% attack doesn't necessarily need 51% of nodes to work.
51% attack needs more hashrate than the rest of the miners combined.
Of course this can't be happen now because he can't get 51% of total computers installed bitcoin?
Even if you change the bitcoin source code and compile it, you'll still need to get people to install it which would be a very uphill task.
Also, if your revised bitcoin node does not follow the bitcoin nodes consensus rules, it will most likely be IP banned by other nodes it attempts to pair (peer) to.
Any node software that does not follow the bitcoin consensus rules is NOT a bitcoin node, and it will form its own network.
For example, if your revised version attempts to spend more coins than inputs, the transaction will not be rejected by the nodes it relays the transaction to and the transaction will not be relayed to other nodes, therefore any node running your version of the software will form their own network
different from
the Bitcoin network.
After the first block reward halving from 50BTC to 25BTC in 2012, some miners patched their software to keep mining blocks with 50BTC block reward but the other nodes in the network just rejected the transactions and didn't relay it.
That is what will happen if your software changes any bitcoin consensus rules without you having majority of the node support.
Then, how about early started new coin's case?
Some big guy can take over new coins with over 51% computing power?
It's possible, yes, but what would be the point?