Hi Saroj,
Try this,
CREATE TABLE test1
(ID INT IDENTITY,Val CHAR(2))
INSERT into test1 VALUES('AA'),('BB'),('CC'),('EE'),('FF'),('GG'),('HH'),('II'),('JJ'),('KK'),('LL'),('MM')
select case when LEN(ID)<=2 then right(('000'+convert(varchar,ID)),3) else convert(varchar,ID) end as ID,Val
from Test1
Result :
ID Val
001 AA
002 BB
003 CC
004 EE
005 FF
006 GG
007 HH
008 II
009 JJ
010 KK
011 LL
012 MM
Hope it helps... :)