Hello Mudit,

CDS (Combined defense service) has need graduation. It is not depend on 12th marks. There are educational eligibility for CDS  (Combined defense service)as:-

•Indian Military Academy (IMA) and Officers’ Training Academy - A candidate should be degree from any recognised board.

•Indian Naval Academy (INA): A candidate should have Degree in Engineering from a recognized university.

•Air Force Academy: A candidate should have Degree of a recognized University (with Physics and Mathematics at 10+2 level) or Bachelor of Engineering.

There are educational eligibility for AFCAT (Air Force Common Admission Test) exam as:-

•A candidate should be passed 12th or equivalent exam in maths and physics with 60% Score. (Flying branch and ground duty(technical).

•A candidate should have minimum bachelor degree from any recognised college/educational board.

You can check the eligibility criteria - http://competition.careers360.com/articles/cds-eligibility-criteria

But for AFCAT exam, candidates need to have atleast 60% marks in 10+2 level-
http://news.careers360.com/indian-air-force-afcat-notification-2020-released-check-eligibility-criteria

Hope! This helps.

All the Best !!!