Store Mysql Index in separate .Ibd file? Is there any option to store table index in separate .ibd file? something like file_per_table mode? Becuase my table is growing more than 200gb. Table .ibd file have index for that table also. so If index kept in another file, then table .idb file size will be reduced.

Thanks
In theory it's possible. What you call a table in InnoDB is a B+tree index named PRIMARY. The key in the PRIMARY index is the primary key field(s). 

All secondary indexes are B+tree indexes, too. The key would be the secondary index field(s). The value is the primary key.
(See my slides to get more details http://www.slideshare.net/akuzminsky/indexes-in-my-sql-aleksandr-kuzminsky-https-twindbcom?ref=https://twindb.com/efficient-use-of-indexes-in-mysql/)

Although logically the PRIMARY and secondary indexes are separate they're still stored in one .ibd file (that's assuming innodb_file_per_table=ON). There is no way to store them in separate files.