busy 短语的用法常用的有两个：
be busy with sth 忙于做某事
be busy doing sth 忙于做某事
例如：
1.The plan for the new book is on ice at the moment.I've been busy with too many other things.
写那本新书的计划暂时搁一下,我一直忙于太多其它的事情.
2.He is busy doing his homework.
他正忙着做家庭作业.
单独的busy +to do的结构是不成立的
