In oracle, I know that a user only refer to a shcema. In DB2,is there a user can refer to many schemas

Yes. You can refer it by schema.tablename
eg:
select * from schema1.table1
select * from schema2.table2
select * from schema3.table3


If you create tables/views by USER1, then you are not necessary to refer by schema.tablename (select * from table1 --> will do). But other users have to use schema.tablename.

Regards
Prakash

Yep

And in DB2 for z/OS environment, you can use SET CURRENT PACKAGESET statement to obtain dynamic schema selection.

Cheers, Bill