这两个短语的共同意思是“被…所遮盖”。

当介词宾语为非人为的自然物时,两者可互换。

例如: The mountain is covered with〔by〕 snow all the year round.山上终年积雪。 其区别是：

1、强调点不同。 强调状态时多接with，强调动作时多接by。例如:

1. The mountains are covered with forests. 山上长满了树木。
2. His teeth were never entirely covered by his lips. 他的牙齿从未被嘴唇完全遮住过。

2、用法不同。 当介词宾语为一件较小的覆盖物(如:cloth, book)时,一般要用with,因为此时往往用“人”作为行为施动者。例如：

The table was covered with a table cloth (by me).(我在)桌上盖着一块桌布。