SELECT
T1.CT_ID,
T1.LT_UPD,
T1.CREATED,
T1.LT_UPD_BY,
T1.CREATED_BY,
T1.M_NUM,
T1.ROW_ID,
T1.CURCY_CD,
T1.X_ATTRIB_15
FROM
SIE.C_CLAIM_M_M T1
INNER JOIN SIE.S_IN_CLAIM_M T2 ON T1.PAR_ROW_ID = T2.ROW_ID
WHERE
((T1.TYPE = 'Transaction Reserve') AND
(T2.ATTRIB_03 = 'CLAIM')) AND
(T1.CLAIM_ID = '1-CG9X0S')
ORDER BY
T1.CLAIM_ID, T1.X_ATTRIB_18

Is it not homework?

Some ideas to rewrite the query are as followings....
Although they may influence performance or not, they may improve readability and maintenability.

1) "INNER JOIN SIE.S_IN_CLAIM_M T2" can be replaced by EXISTS, if T2.ROW_ID is unique.
Because, no column of T2 was included in the select list.

2) T1.CLAIM_ID is not neccesary in ORDER BY clause.
Because T1.CLAIM_ID = '1-CG9X0S' was specified in WHERE clause.

3) I couldn't find any reason to use unnecessary parentheses in WHERE conditions.
They harm readability, and may be cause of syntax error at the time of maintenance.

It was working earlier and stuck in between....can any one suggest the best way to optimize this sql query.

This query was working for the last 2 months. can any one suggest what would be the best way to do the performance tuning for the above listed query. the way to optimize the problem.

I, believe, Tonkuma has already answered you on quite a few points that would help speed this query up. If you take his suggestions on the order by and exists subselect, you should see improvement. The other advice for readability and maintenance is, also, spot on.
Dave

Its system generated query as I told earlier for the last 2 months it was working properly and giving prompt results but this time i am facing the problem of long-running query. kindly suggest ....both tables are properly indexed.

- reorg and runstats tables used in the query;
- do not assume that your "system" created a perfect query. listen to suggestion given here;
- do not assume that existing indexes are actually used just because you think they are used.
index usage should bechecked by proper db2 tools.