Hello Nagesh,

Being a police inspector is comparitively easy, but being a part of CBI is quite tough, you must join civil services first, i.e. taking the UPSC exam and then become an IPS officer. SSC Combined Graduate Level Exam is another exam that you will be needing to appear.

for more information please refer this answer:

https://www.careers360.com/question-what-is-process-to-join-cbi-which-has-more-power-cbi-officer-and-ips-officer

You may refer the official website for more information:

http://www.cbi.gov.in/employee/recruitments/vacancy_cbi.php

Hope this Helps