suppose, if i lost password of admin user then how can i retrieve it? because their is no option show to get it back like "forget your password or lost your password" even after filed login.
If you have access to the database, you can read it with the following SQL query:
select password from res_users where login='admin';
On the other hand, if you have admin access to OpenERP (which requires having the password, which may be too late for you...) you can go to Settings -> Configuration -> General settings, and in the "Portal Access" section, check the "Enable password reset from login page" option. Then you will get a "reset password" link from the login page which will send a link by email to the email address linked with the user attempting to log in, if you have also configured the email gateway. This works in V7.
In OpenERP 7, go to Settings > Users and select the user you want to reset the password for. You will see a button labeled "Reset password" in the top right corner that will send an email to the email address of the user with a new password.
An email smtp server needs to be set up in OpenERP for this to work.