When I want to vote on some proposals, I need to lock some MKR tokens. Does it mean that I withdraw my MKR tokens, then the result of voting may change even after it has finished?
Does Continuous Approval Voting mean endless voting?
Does it mean that I withdraw my MKRs then the result of voting may change even after it has finished?
If the voting for a specific proposal has finished (and has become the governing proposal), then it will be executed on chain. It will not matter remove your MKR tokens or leave them.
Does Continuous Approval Voting mean endless voting?
Not necessarily. Continuous Approval Voting means that competing proposals may be introduced any time. You, a MKR holder, can vote on any proposal at any given time (even old ones). However, only the proposal with the most votes will be the governing proposal.
The is in contrast to a non-continuous approval voting mechanism where you may only get to vote on one of two options.
You can read all about the voting system here.