First of all thank you to help me but i cant give clat exam because i m pursuing my graduation .clat is for 12th cleared students for 5yr integrated course but i want 3yr one llb course which is not available in any of national university across india.Thats the problem .I want to know about the entrance exams for 3year llb program and their colleges

Some of the best colleges for LLB are

National Law School of India University (bangalore)

National Law University ( New Delhi)

Symbiosis (Pune)

NALSAR University of Hyderabad 

Rajeev Gandhi School of Intellectual property(Kharagpur)

National Law University (jodhpur)

Jindal Global Law school (sonepat)

UPES (Dehradun)

Christ University Law School

You need to decide whether to go for government institutions aur private ones. 

To get admitted in good colleges you must go for CLAT entrance examination.

There are 12 National law Universities and for them you need to clear CLAT, there is no other option.

However, there are other colleges that  conduct seperate entrance examination or give admission on the basis of 12th results.