小木虫和网上都有模板 楼主你搜下就OK了  祝好！

可以参考
https://muchong.com/html/201205/4501854.html

https://muchong.com/html/201503/8592929.html

委婉的说一下就好，当然你不交钱一样的不被发表，不过最好说一下

Manuscript Number：XXXXXX
Manuscript title: XXXXXX

Dear editor,

Please excuse me for taking some of your time. We submitted a paper (manuscript number: XXXXXX) to XXXXXX on X X 2015. The paper is _____ now. We would indeed very much like to publish in your Journal. However, due to some technical reasons (there are obvious errors in the derivation of the theoretical model) and now we hasn't figured out how to address, we decided to withdraw our manucript at present.

I apologize for any inconvenience caused by the withdrawal of this article. Once again, thank you very much for your consideration and time.

With kind regards,
Yours sincerely,
XXXXXX，