两者，都表示该做却没做的事。
区别在于，should have done. 是对现在完成时的虚拟语气，对事件的发展造成的一定的影响，或既定效果。
should do. 是对一般现在时的虚拟。
虚拟不能说是对过去，现在，将来的虚拟，而是一种时态。由句意判断，这个句子表达的意思是发生在什么时候。
另外将来时态的虚拟，直接是 will, 或者现在进行时表示将来。
虚拟语气大概就这些了，也是语法中相对难的。，中，高考一般2题左右、
望采纳
前者是说 现在应该做xxx
后者是悔过， 说 原来本应该做xxx.
在语气上比had更委婉，可用于其他人称，比如 You
I should have been angry.
should have+完成时态
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:(不过考试建议你还是多用虚拟语气)
It is a shame that the rain spoiled our piic.
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.
他损失这么多钱，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么长命。
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。)
欢迎探讨词法语法问题。
都不是虚拟语气，楼上正解。SHOULD只有用在SUGGEST,WISH,DEMAND后年的宾语从句里才表示虚拟语气。
前面一部分是用在后面的主句里。后面一部分是用在if条件句里的。
举个例子：
If she had reviewed the text yesterday, she would have passed the exam.如果她昨天覆习了课文，她是可以通过考试的。
在例句中，had reviewed用在if条件句中，would have passed用在主句中。
在被动式中用should be done
高考热点(⊙o⊙)~
要看前面的部分是什么。
若：i have told you that you shouldn't do this.句中的should仅仅表示应该的含义。为情态动词的考查范围。
如果与虚拟语气有关，比如：
it is high time that you should do your own work.
以上两句均为should做宾语从句的部分，但是很明显用法不同。
关于should，一般就考察做情态动词表语气如：you should have done this.表责备语气。或是考察关于虚拟语气：he requires that you (should) finish it.
should和would的用法：
should常译作“应该”，would常译作“愿意；会”。
1. should和would都可用于疑问句，表示征询意见或提建议。但它们比shall和will更委婉。如 Should we open the window? / Would you mind asking you so many questions?
2. should和would都可用于肯定句或否定句。
(1)should译作“应该”，表示义务或推测。如 We should protect our environment. (义务) / You shouldn’t know him. (推测)
(2)would译作“愿意；会”，表示过去的意愿或意志。 如 She said she would bee a volunteer. / He promised that he wouldn’t fall behind others.
3. should和would都可作助动词，它们是shall和will的过去式，用于过去将来时，译作“将要”。should用于主语是第一人称，would用于主语是任意人称。如 He said we should / would move to the second floor.