定语从句that可以省略的情况具体如下：
1．用作代词，代替前面所指的事物，常见于表示比较关系的状语从句中，例如：
It is warmer in the south than(that of)the south.
2．引导名词性从句作宾语，即宾语从句，例如：
She said(that)she would come.
I suggested(that)we(should)go home.
3．作关系代词，在定语从句中作表语或宾语，例如：
Can I have the records(that)I lent you?
He is just the man(that)you talked about.
4．在 way（意为manner）后面，that 意思为 in which，例如：
Do it the way(that)I showed you.
5．在表示个人对事物反应、表示重要性或迫切性的adj后所接的从句中，例如：
I am glad(that)you are right.
It is obvious(that)they are happy together.
6．so that, so…that, such…that, 结构中，例如：
I came to see you so(that)you would know the truth.
She had so many children(that)she didn’t know what to do.
I was having such a nice time(that)I didn’t to leave.
7．用于表示时间的词后面，整个短语相当于when，例如：
I joined the army the year/month(that)my father died.
I thought her nice and honest the first time(that)I met her.
I though her nice and honest when I met her.
8．如果定语从句中的谓语是there is，作主语的关系代词that也常省略，例如：
This is the fastest train(that)there is to Beijing.