由于这个句子实际上的主语（if/ whether 引导的主语从句）太长，而用it作为句子的形式主语，make是句子的谓语
It makes no difference whether he will attend the meeting or not. 他是否会参加会议都无关紧要。
It makes no difference if he doesn't know me.
他知不知道我并没什么区别。
it构成的主语从句
（1）由连词that引导的主语从句，在大多数情况下会放到句子的后面，而用代词it作形式主语。如：
It is well-known that the earth moves around the sun. 众所周知，地球围绕太阳转。
需要注意的是，it作形式主语代替主语从句时，要注意和as引导的定语从句的区别。试比较：
It was reported that the US was under the terrorist attack. （主语从句，有that，无逗号）
As was reported, the US was under the terrorist attack. （定语从句，无that，有逗号）上两句意为“据报道，美国遭到恐怖分子的袭击”。
（2）常见用it作形式主语的复合句结构
<a>It is a fact （a good idea / a pity / a shame / no wonder / good news…）that…如：
It's a pity that you missed the film. 你没有看那部电影真是太遗憾了。
<b> It is necessary （clear / true / strange/ important /wonderful / possible / likely…）that…
需要注意的是，这类主语从句中，谓语动词很多为“（should）＋动词原形”，即要用虚拟语气。如：
It is necessary that you （should）master the computer. 你很有必要掌握电脑。
It is important that a student learn English well. 学生学好英语很重要。
It's clear that they badly need help. 很明显，他们急需援助。
It is likely that a hurricane will arrive soon. 飓风很可能马上就要到达了。
<c>It is reported （well-known / hoped / thought / expected /said /believed/decided /suggested /ordered…）that…如：
It is said that he was killed in the earthquake. 据说他在地震中丧生了。
<d>It seems （happened / appears / doesn't matter / makes no difference / …）that …如：
It seems that they will win the game. 看起来他们好像会赢得这场比赛。
It makes no difference whether he will attend the meeting or not. 他是否会参加会议都无关紧要。