helpful可以跟for也可以跟to。helpful用作形容词，有给予帮助的，有益的，愿意帮忙，(事物）有助于改善局面的，有好处的等含义。helpful to和heplful for都有"有助于"的意思，但helpful to较常用于接人，而helpful for也可以接人，但多用于接sth或doing sth，表示"对....有益"。

be helpful to ，对…有帮助的。例句：He is always very helpful to his mother。他对他母亲总是很有帮助。This dictionary is very helpful to your English study。这部词典对你学习英语很有帮助。

be helpful for ，对....有益。例句：Don't throw it，it is helpful for us to repair the bike。别扔了它，它对我们修自行车有帮助。It was helpful of you to do that。你那样做真是助人为乐之举。

helpful其他用法：be helpful in doing sth.对做某事有帮助。例：We hope this leaflet has been helpful in answering your questions。我们希望这个宣传单可以帮助您找到您想要的答案。be helpful有帮助的。例：She is intelligent，outgoing and helpful。她聪明、开朗、乐于助人。