We use 了解when we know about a particular situation or event, or the information we have about it; whereas we use 理解 when we try to understand something that is difficult or complicated. As you can see, they are totally different and they mean different things. Evans denied all knowledge of the robbery. 依文否认了解这次抢劫案(You can use 理解here) I had no knowledge of this whatsoever until The Times contacted me. 我对此事一点都不了解，直到TIME时报联系我。(You can use 理解here) I didn't understand the teacher's instructions. 我不理解老师的指示 (You can use 了解here) BTW, 了解 and 理解 have different meanings in different situations, For example, 你不了解我 means that you don't know me very well, which implies that you know something about me, such as where i live, what my job is, what my personality is etc 你不理解我 implies that you don't understand how i feel or you can't understand my problem, situation etc

了解 = understand, literally, "finished untying" 理解 = to understand through a series of deduction, logic etc. Literally, "[using logic" to untie".

了解 is means you understand the general process, or something not deep, for example:你们刚认识，应该互相了解(you have just known each other, you guys may try to know more about each other) 理解 is more about the meaning behind of the things or theory,such as 这篇文章内容太深，学生们理解不了(this article is difficult, the students cant understand it well)

理解： really understand "why" . For example: 你理解这个问题吗？ = do you understand this question? 了解： know something . For example：你了解这个问题吗？= do you know/hear about this question?

I wanna teach u …… but i dont know how to express by English (ˇˍˇ)