1. 两者均可指人，有时可互换(包括当先行词为 all, anyone, someone等，同时也包括先行词受the only等的修饰时)：
All that [who] heard him were delighted. 所有听了他讲话的人都很高兴。
He is the only one among us that [who] knows Russian.他是我们中间唯一懂俄语的人。
Anyone who [that] is over sixteen is allowed in. 任何超过十六岁的人都允许进去。
It is impolite to turn your back on someone who [that] is speaking to you. 人家跟你说话，你把背朝人是不礼貌的。
2. 但是在下列情况，通常要用 that：
①当先行词是一个既指人又指物的并列词组时：
I made a speech on the men and things that I had seen abroad. 我就我在国外所见到的人和事作了报告。
②当先行词是who时(为避免重复)：
Who was it that won the World Cup in 1982? 谁赢得了1982年的世界杯?
③当关系代词在定语从句中作表语时(可省略)：
Tom is not the boy (that) he was. 汤姆这孩子已不是以前那个样子了。
3. 但是在下列情况，通常要用 who：
当先行词为 those 且指人时，英语习惯上要用 who 来引导定语从句。如：
Those who do not wish to go need not go. 不愿去的人不需要去。
Those who couldn’t walk were carried on stretchers. 那些不能走的人都用担架抬着。
It is said that those who eat the most are the least healthy. 据说吃得最多的人身体最差。
Only those who had booked in advance were allowed in. 只有那些预先订票的人可以进去。
The plan was supported by those who wished to listen to more good English. 这计划受到想多听好英语的人的支持。
Let us spend a few moments in silence so that / in order that we remember those who died to preserve our freedom. 让我们默哀片刻，以缅怀那些为维护我们的自由而牺牲了的人们。
注：偶尔也可见到在 who 之后用 that 引导定语从句的用例，但相当少见。如：
The danger is that people who pay their bills on time will be lumped in with those that don’t. 危险的是那些及时付账的人将会同那些不及时付账的人混在一起。
