“大学同学" 用英语是"College Classmate", 你可以只是说"classmate (同学)" 我不经常听人说"College classmate".

college classmate 如果说到具体大学，可以说 He's my classmate at Harvard University. 参见 http://www.theblaze.com/contributions/obama%E2%80%99s-college-classmate-the-obama-scandal-is-at-columbia/