複雜的名詞可以使用 complexity（聽發音）、complication（聽發音）或 intricacy（聽發音）來表達，例如複雜性理論英文是 complexity theory。
另外有一個英文單字 complex（聽發音）拼法也很類似，同樣都是複雜的意思，且可以當名詞、動詞或形容詞使用，例如 complex thing 就是複雜的事情。
複雜英文造句練習
You make things too complicated, please relax.你把事情太複雜了，請放輕鬆。
This mathematical problem is too complicated, I counted no answer.
這題數學太複雜了，我算不出答案。
Jack always have a way to simplify complicated things.
傑克總是有辦法把複雜的事情簡化。
The relationship between Tom and Adam was very complex, difficult to understand.
湯姆跟亞當之間的關係錯綜複雜，讓人難以理解。
This dish practice is not complex as you might think.
這道料理的做法沒有你想像中的複雜。
Don't make the thing become more and more complex.
不要使事情變得越來越複雜。
This thing a little complicated, and I'll explain.
這件事情有點複雜，我來解釋。
Just need to find ways, more complex things also can be solved.
只需要找到辦法，更複雜的事情也能得到解決。
This system is very complex, not one engineer can maintain.
這個系統非常複雜，不是一位工程師能夠維護的。
I think the traffic in Taipei is quite complicated, so I do not like driving in downtown Taipei.
我認為台北的交通相當複雜，所以我不喜歡在台北市區開車。
For grandfather, the operation of the smartphone is too complicated, so he does not like it.
對於爺爺來說，智慧型手機的操作太複雜，所以他不喜歡。
Humans know how to use supercomputers to predict complex weather.
人類懂得利用超級電腦預測複雜的天氣。
This operating system has a very complex membership rights management function.
這套作業系統有非常複雜的會員權限管理功能。
The too complicated checkout process will allow consumers to abandon the purchase.
太過複雜的結帳流程會讓消費者放棄購買。
The boss thinks the project is too complicated and the cost is too high.
老闆認為這項專案太複雜，成本太高。
Many people can not calculate complex mathematical problems.
許多人無法計算複雜的數學問題。
Nutrition science is actually very complicated.
營養科學其實非常複雜。
The new car has a lot of high-tech, maintenance is also quite complex.
新款的汽車有非常多高科技，維修起來也相當複雜。