Is there is any way by which I can find the constraint related to a table under db2 v8.1

db2look is the nicest/easiest way, if you use it with '-e' and '-a' it'll dump out all the ddl for the database, including constraints.

You can also monkey around with the system catalog tables, as described in the appendix of SQL Ref vol 1. SYSCAT.TABCONST is the one I think you want.

check -> SYSCAT.TABCONST table.
It contains a row for each unique (U), primary key (P), foreign key (F) and table check (K) constraint.