意思一样,但是用法区别：in addition to是介词短语,只能单独使用,通常放在句子开头,并用逗号隔开.In addition to giving a general introduction to computers,the course also provides practical experience.
但是besides既是介词也可以是副词,如：there were two other people at meeting besides(介词) Jack.2,it is such a long way.Besides,i haven't got enough money left.