On slave status some time it shows seconds_behind_master 0 and suddenly 16555 and again 0 ,is it any type of bug or what can any one please elaborate why it happen i am using percona server 5.6.
The seconds_behind_master status variable is just an estimate. You likely have DML (i.e. ALTER TABLE) or a large bulk INSERT/UPDATE/DELETE that just finished running. MySQL will see that, and guess that it will take a certain period of time (16555 seconds in your case), but it ends up going much quicker in a lot of cases.