quantity 之具体的数量,amount 大量的.

quantity 是可数的数量 amount 是不可数的数量

amount与不可数（uncountable）、无生命（inanimate）的名词连用，

如：

The amount of work I did yesterday was twice the amount I did today.

She spent a very large amount of money yesterday.

quantity与可数（countable）或不可数（uncountable）、无生命（inanimate）的名词连用，

如：

There are large quantities of apples on the market.

A large quantity of fuel has been used.