"An additional review" I have recently recieved the reponse from the editor of the submitted journal. At the beginning, the editor wrote "The manuscript requires revision and probably an additional review before a decision can be made on its suitability for publication." . I'd like to know "an additional review" means the editor will find another reviewer? Or just after recieving the revision, he won't make a decision himself but send the revision to the present reviewers? Thanks a lot.
The editor is probably referring to another round of review - more than likely sent to the same reviewers, though this statement does not explicitly say so. Essentially, based on the previous round of reviews it seems the paper need not be rejected outright but requires some major revisions such that reviewers need to evaluate whether those revisions alleviate their concerns.

If the editor meant that it was to be sent to a new reviewer they would have said "an additional reviewer" rather than additional review.

Of course, it's also possible that the editor messed up the English, though I think that is unlikely in this case; the situation sounds pretty clear because of the need for revisions. If a paper needs to go to another reviewer for an editor to make a decision that would usually happen before any revisions (this would normally happen if the previous reviewers disagree, or if the previous reviewers indicate in their review that there are parts of the paper they did not feel qualified to assess).