Is it okay to include a graduated phd student as a reference in resume/C.V? I'm trying to apply for a PhD and want to include references in my resume. Is it okay to include a PhD student, one who has gotten a degree and has worked in our lab,and is currently working in industry, as a reference?
Yes, they can, but consider whether they're the best choice:
A referee needs to be your champion. A lab mate who you've never worked with probably can't do that, because they don't have a working relationship with you. Someone you've worked with can. (It's unclear which case applies here.)
Senior referees carry more clout than junior referees, so that's something to keep in mind.
Having referees from both industry and academia can be useful—it depends who the recipient is: A theoretician will surely be less interested in a referee from industry than someone more applied.