How do i insert into a table which has a foreign key reference of composite key?
For example:
Table A:
A1col varchar(10)
A2col varchar(10)

Both A1col and A2col are primary key

Table B:
B1 col varchar(10)
A1col varchar(10)
A2col varchar(10)

A1col and A2col refer to table A.

How do i insert in table B using hibernate?

If you are using Annotations, maybe you can check the explanation of the @IdClass annotation at:
http://www.hibernate.org/hib_docs/annotations/reference/en/html/entity.html#entity-mapping-identifier

Then you should insert by simply assigning values to the properties of the entity bean and persisting it.

No ..i am not using annotation.