How can i add custom field inside custom post taxonomy?

There is a plugin for that http://wordpress.org/extend/plugins/taxonomy-metadata/

OR

Adding custom meta fields to a taxonomy requires three separate functions: one to add the field to the Add New page; one to add the field to the Edit Term page; and one to save the values of the custom field from both pages.

You can also do this by code yourself like this :

https://pippinsplugins.com/adding-custom-meta-fields-to-taxonomies/