Question

In addition to 和 besides 的用法一样吗？

Answer 1

In addition to整个词组相当于一个介词，所以to的后面要接宾语。例如:

In addition to native plants, this garden contains numerous trees and flowers from overseas.

除了当地的植物之外，这座花园还有无数来自海外的花草树木。

"In addition to" 后面可接句子而besides不能。
besides is a preposition and adv. It can be used as a preposition, followed by noun.

As well as is a phrase, followed by noun.

1. In addition to what I just described above for you, you can look at other materials.

2. Besides, I'd like you to know that I will be late for next meeting.

Answer 2

除...之外(还)
In addition to French, he has to study Japanese.
除了法语外,他还得学日语。
副词 ad.

1.此外,而且,加之
The driver couldn't see either. Besides, the roads are nearly impassable.
刚才司机也看不清楚。而且这些路简直无法通行。
Besides, I want you to promise me one thing.
此外,我要你答应我一件事。
2.在其他方面

介词 prep.

1.在...之外,除...之外
What has he done, besides reading the paper?
除了看报,他还做了什么?
He had other people to take care of besides me.
除我之外,他还要照顾别人。