"Its method is very simple" 的英文表达是 "Its method is straightforward"。
"straightforward" 是英语中常用的形容词，意思是简单易懂的，不复杂的。
例句：
The instructions for assembpng the bookshelf were straightforward. (组装书架的说明很简单易懂。)
The solution to the math problem was straightforward once I understood the concept. (一旦我理解了题目的概念，数学问题的解决方法就很简单了。)
The recipe for making this dish is straightforward and easy to follow. (做这道菜的步骤很简单，易于按照。)