show up 和 turn up 都是动词短语，当表示“出现，露面”含义的时候，是同义词。
show up
英文含义：to come to or arrive at a place; make an appearance
We waited for three hours，but they didn't show up.
turn up
英文含义：If you say that someone or something turns up, you mean that they arrive, often unexpectedly or after you have been waiting a long time.
He had turned up on Christmas Eve.
总结
1.Turn up 和show up相比， 有一种突然出现或等了很久之后才出现的含义。
2.在使用的时候，show up 在外刊中比turn up 要多得多，所以表示“出现”含义的时候，建议选show up 会更好。
