If you want to delete the department, you need to move all the employees in the department to other departments or delete the employees:
1. Desktop Client: The administrator logs in to Admin Panel (oa.dingtalk.com)-[Contacts] - [Department], and then click [Modify] - [Delete].
2, Mobile app: administrator login [Mobile app] - [Contacts] - [Organization Management] - [Company Contacts] - [Manage Employee & Department] - select the department to be deleted - [Edit] - [Delete Department].