Occupy 和preoccupy都表示“占据；占领”，二者有何区别？

当然有。看下面的解释：

To occupy is to inhabit, or to be busy with.显然，occupy是指空间上的、物理上的占领；占据，也有“忙于做某事”的意思

如： He occupies the second floor. She occupied herself with routine office tasks.

To preoccupy is to dominate the mind of someone to the exclusion of other thoughts. 而preoccupy是某个念头、想法“占据；盘踞”了你的内心或注意力，从而是你忧心忡忡或是全神贯注。

如：His mind was preoccupied with plans for his holiday.