高中英语 It is + adj+that……后面是不是只能跟虚拟语气？

不是只能跟虚拟语气的. 你要分清什么时候才用虚拟语气
虚拟语气用来表示说话人的主观愿望或假想，所说的是一个条件，不一定是事实，或与事实相反。
如果不是表达岩碧那些意思的话是不用粗搭举到虚拟语气的
例如:

It is strange that he had made a mistake. 奇怪的是他犯了一个错误。
这是一个陈述句，就是陈述一个事实：他犯了错误让人有点奇怪。
It is strange that he (should) have made a mistake. 他居然犯了一个错误，真令人奇怪。

这是虚拟语气，说话者是在责备他本不应该犯错。
It is/was ＋形容词/名词＋that主语从句多数情况下用虚拟语气，表达一种要求，命令或者责备，但是如果只是表示陈述一个事实而不是强烈的感情，完全可以用一般的陈述语气。

以下为词典原句:(不过考试作文中建议你还是多用虚拟语气)
It is a shame that the rain spoiled our picnic.
真可惜，这场雨把我们的野餐给搅了。

It is a pity (that) he lost so much money.
他损失这麽多钱，真是遗憾。

He was a very brave man and it is surprising that he lived so long.
他是一个非常勇敢的人，而令人惊讶的是他活得那麽长命。

It is strange that nobody knows where he lives .
真奇怪，谁也不知道他住在哪里。

附：虚拟语气用在主语从句中有以下几种情况：
1.在句型 "It is important (necessary, strange, impossible, natural) that .... " 中，that后面的从句中的谓语动词用：(should) + 动词原形。 如：
It's necessary that we should have a walk now. 我们有必要出去散散步。
It's natural that she should do so. 她这样做是很自然的。
It's important that we should take good care of the patient.
重要的是我们要照顾好病人。

2.在句型"It is a pity (a shame, no wonder, better) that .... "中，that 后面的从句中的谓语动词用: (should) + 动词原形。 如：
It was a great pity that you (should) have made so many mistakes in your math exercise. 太遗憾了，你居然在数学练习中犯了那么多错误
It will be better that she stay with her grandmother.
她和她的祖母在一起就好了。

3.在句型"It is suggested (requested, proposed, ordered) that .... "中，that 后面的从句中的谓语动枝漏词用：(should) + 动词原形。 如：
It was suggested that the sports meet be put off until next Saturday.
大家建议把运动会推迟到下星期六。
It is desired that we (should) get everything ready by tonight.
希望我们到今晚将一切准备就绪。
It was ordered that the medicine be sent there by plane.
命令马上用飞机把药送往那里.
(个人认为上面的第3种情况基本都要用虚拟语气，因为这里都是表示命令或要求，而第1和第2两种则视说话者要表达的意思决定。)

后常用should+动型启察词原形虚拟，卜茄should一般可省，但表示竟然含义是旁手不可省
It is natural that he (should) win the game.

不一定
desire等用如It is believed that