I Don't have PFILE or SPFILE just have a backup of init.ora and database is down I have lost PFILE  and don't have backup also, just have a backup of init.ora and database is down and not starting up. Does init.ora backup is useful? If yes then how to use it to create pfile or to startup database??
please any solution,
any help will be highly appreciated.
yes, backup of your parameter files is a smart thing to do, like backing up your database is a smart thing to do. If you still have an alert log file of your database, you can extract the parameter settings from there and use them to create a pfile using good old vi or whatever simple text editor you like.
Most important parameters are 


instance_name 
db_unique_name
control_files


Once your parameters are complete, you can verify them by trying to startup the database.

ORACLE_SID={YOUR_ORACLE_SID}
. oraenv
sqlplus / as sysdba
startup nomount pfile={your_pfile_full_name}


If this succeeds, your parameters are good enough to start an instance. Now see if your control_files parameter is OK:

alter database mount;


if your database mounts, you have access to your control file[s].

alter database open;


you could be back in business by now.
Since it is smarter to use an spfile, now is the time to create your spfile:

create spfile from pfile='{your_pfile_full_name}'


This creates the spfile for this instance with the default name in the default location (${ORACLE_HOME}/dbs/spfile${ORACLE_SID}.ora). Shutdown your database and start it without specifying a pfile or spfile. It should select the just created spfile and give you back your database as it was before.