that引导主语从句能省略吗？由that引导主语从句不能省略 。请看例句：
That he has told lies is quite clear. 他说了谎，这一点很明显 。
“That he has told lies”是主语从句，在句中作主语，看作单数，谓语动词用单数 。如果省去that，句子就成为：He has told lies is quite clear.句中便有了两个谓语，has told和is，这样就会引起理解上的混乱，显然是错句 。
另外，由that引导的主语从句，往往被放在句尾，前面则用it充当形式主语 。如：
It goes without saying that he loves her at the first sight. 毫无疑问他对她一见钟情 。
It is sheer luck that he survived the accident. 他在事故中逃过一劫纯粹是运气 。
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【主语从句可以省略吗】.
主语从句that可以省略吗语法上不能省略，因为省略了that，原本的从句变成了一个句子了，那么就导致有两个谓语，也不文不类 。如 （That） he orders takeout everyday is his habit.他习惯了每日都点外卖 。
英语主语从句，后面从句什么时候能省略主语？who 或者是that在引导主语从句的时候，都是不可以省略的 。不仅是主语从句的主语不能省略，这些引导词也不能省 。who说明后面这个句子是对主语提问 。that说明这是陈述句 。而不是疑问句 。所以才不需要疑问词 。
主语从句的主谓成分能否省略？一、状语从句主谓成分的省略，须遵循下面原则：
（一）当从句的主语与主句的主语一致时，从句可以省略主语，从句的谓语动词采用其V-ing结构 。例如：
Although working very hard, he failed in the final exam. (Although he worked very hard,…)
After taking the medicine, she felt much better. (After she took the medicine,…)
If going there by air, we’ll have to pay twice the fare. (If we go there by air,…)
（二）当从句的主语和主句的主语一致时，若从句的谓语动词是系动词be或包含be的某种形式，此时从句的主语和be动词通常可以一同省略 。常见于以下几种形式:
1、连词+形容词
Whenever (she is) free, she often goes shopping.她有空就去逛商店 。
Work hard when (you are) young, or you'll regret.少壮不努力,老大徒伤悲 。
She hurried out of the room, as if (she was) angry.
2、连词+名词
While (he was) a young boy, he was always ready to help others.他在孩提时代就乐于助人 。
He could write poems when (he was) yet a child.
3、连词+现在分词
While (she was) walking along the river bank, she was singing a pop song.她沿着河堤边走边唱着流行歌曲 。
The boy is running impatiently here and there as if (he is) searching for something lost on the sports ground.这男孩很不耐心地在操场上到处跑着仿佛在找什么东西 。
4连词+过去分词
If (it is) well read, the book will give you much to think.
Unless (they were) asked to answer questions, the students were not supposed to talk in Prof. Li’s class.
5连词+不定式
He stood up as if (he were) to say something.当时他站起来好像要说什么 。
He wouldn't solve the problem even if (he were) to take charge.即使他来负责,他也解决不了这个问题 。
6、连词+介词短语
She looked anxious as though (she was) in trouble.她看上去很焦急,好像遇到了麻烦 。
He looked everywhere as if (he was)in search of something .他到处看似乎在找什么东西 。
He came across the picture while (he was) on a visit to New York.
（三）若从句的主语和主句的主语不一致，但和主句的宾语一致时，从句中的主语和be动词亦常可省略 。例如：
Father advised me not to say anything until (I was) asked.
Granny told the children not to talk while (they were) eating.
（四）当从句的主语是it, 且谓语动词是be或包含be的某种形式时, it和be常可同时省略 。例如:
If (it is) possible, he will help you out of the difficulty.如果可能的话,他会帮你摆脱困境 。
You must attend the meeting unless (it is) inconvenient to you.除非情况对你来说不方便,否则你必须出席这次会议 。