Redmine Importer allows importing issues in bulk from .csv files. Fields will default to name-based mapping but can be overridden at the confirmation screen. Existing issues can be updated, and issue relationships and custom fields are supported.
similar to importer plugin(http://www.redmine.org/plugins/importer).
Download the plugin to your application/root/folder/plugins directory. Be sure to maintain the correct folder name, ‘redmine_importer’.
Run ‘rake redmine:plugins:migrate RAILS_ENV=production’
Restart your redmine as appropriate (e.g., ‘rails s -e production’)
Go to the Admin/Projects/../Modules
Enable “Importer”
credits Leo Hourvitz