So, both mean 'to finish, complete sth.'. I guess 完毕 is more formal, because the examples given for it include things like court cases, whereas 完成 seems to be things like homework/general tasks. Any other differences between the two?! Regards, A very thankful Hashamyim
完成 mainly mean 'accomplish' ('成' in '完成' means successfully or become) ; 完成 is mostly for 'something people do'
完毕 mainly mean 'end' ('毕' in '完毕' means 'end'); 完毕 is mostly for 'something that happens'
完毕 syn 完結 (ended)
完成 (v) to complete; to accomplish; to fulfill; to finish; to succeed
完成 can be used with or without object
E.g. 已经完成工作 and 工作已经完成 are both correct
完毕 (v) to end; to finish; to complete
完毕 doesn't take object
E.g. 學期完毕; 工作完毕 (you can't say 完毕學期 or 完毕工作) (學期 and 工作 are both subject in the phrase )
When you want to say an event is 'ended', you have to use 完毕
When you want to say a task is 'accomplished', you have to use 完成
Do not use 完成 for 'an event is ended' (學期完成 is incorrect, )
完毕 - Finish 完成 - Complete
They're slightly different even in English. See What is the difference between 'finished' and 'completed'?
Grammatically, 完毕 is often used as a complement. 完成 can be used as an transitive verb or a noun.
For example, we say 准备完毕， 准备 is a verb and 完毕 is its result complement. When we say 准备完成, we use 完成as an transitive verb, so we should add an object like 准备完成这项工作. 完成 sometimes can be used as a noun word, like 这项工作的完成. We don't usually say 这项工作的完毕. That is to say, 完毕 is not used as a noun normally.