I want to make more than one accountability member for a project.

is this possible to do that if yes kindly suggest how to achieve this one.

Dear Pankaj, 

It is not possible yet to set multiple users as accountable for a work package. As a workaround you can create a group and set this group as accountable. Here is the description for managing groups. 

There is a feature request about multiple assignees without group creation which might be interesting for you: https://community.openproject.org/projects/openproject/work_packages/30105/activity

Best regards
Samantha