首先我们来看下fail to do sth和fail in doing sth的大致意思：
fail to do sth：词性为短语，fail to do sth 是一个动词短语，由动词fail和不定式to do sth构成。
fail in doing sth：词性为短语，fail in doing sth 是一个动词短语，由动词fail和介词in以及动名词doing sth构成。
通过下面的表格我们了解下fail to do sth和fail in doing sth的含义、发音和用法
接下来让我们看下fail to do sth和fail in doing sth的用法区别：
1.结构上的区别：fail to do sth是动词+不定式的结构，而fail in doing sth是动词+介词+动名词的结构。
例子：
- They fail to complete the task.
(他们fail to complete the task.)
- He fails in understanding the concept.
(他在学习上fail in understanding the concept.)
2.动作完成与否的区别：fail to do sth表示未能完成或实现特定的动作或任务，而fail in doing sth表示在进行某项活动或任务中失败。
例子：
- I fail to submit the report on time.
(我fail to submit the report on time.)
- He fails in trying to fix the computer.
(他fail in trying to fix the computer.)
3.时间顺序的区别：fail to do sth强调动作未能在将来完成，而fail in doing sth强调动作在过去或正在进行中失败。
例子：
- She fails to meet the deadline for the project.
(她fail to meet the deadline for the project.)
- He fails in persuading his boss to give him a raise.
(他fail in persuading his boss to give him a raise.)