一、英语里 it 和that具体指代的区别：
it／that二者均可用作代词, 指代前面提到的名词。一般说来, it指代同名同物; that
则指代同名异物。
I have lost my umbrella; I'm looking for it. （该句中it就是指前面的my umbrella）
The umbrella you bought is cheaper than that I bought. （替代词that在该句中特指“the umbrella I bought”, 以区别“the umbrella you bought”）
二、其他区别：
1、 that用来指代同名异物, that为特指, 相当于the ＋名词。that所指代的名词的修饰语往往是the ／this ／that。
The water in the cup is hotter than that in the pot. （该句中that可以换成 the water）
2、that既可以代替不可数名词也可以代替可数名词单数, 代替可数名词复数时用 those。
Mary's handwriting is far better than that of Peter. （that代替不可数名词 handwriting）
These pictures are more beautiful than those. （those代替可数名词复数 pictures）
3、 that只能代替事物而不能代替人。
That on the table is mine.
4、 it可以替代句中的不定式或从句等, 充当形式主语或形式宾语。that无此用法。
It is known to everybody that the moon travels around the earth once every month.
I found it hard to get on with her.
5、 it与that均可以替代上文全句的内容或部分内容。
He has saved my life; I'll never forget it. （it代替第一分句）
Tom is painting his house. I am told he does it every four years. （it代替前面分句的部分内容painting his house）
Let's say we meet here at three o'clock. That ought to give you time to buy everything. （That代替前面表述的内容）