What is the procedure to Join CBI after passing XII standard?????

Sorry to say that you can’t join CBI after12th standard qualification, so I will suggest you to complete graduation first

You first need to complete Graduation and than apply for the SSC Combined Graduate level exams.

SSC – CGL Exam Eligibility:

Education:
- Must have passed Graduation in any stream from any of the recognized university
-No Minimum Percentage is required in Graduation

AGE-
Minimum 18 years
Maximum 27 years
OBC gets 3 years and SC/ST gets 5 years age relaxations

Exam Pattern:
The exam pattern is as follows –
Preliminary Examination.
Main Examination