This paper attempts to introduce the development contents of a steering control system using the displacement difference ridge tracking method of a self-propelled onion harvester, a representative bulbous equipment. Currently, the self-propelled onion harvester is operated manually, and it is easy to automate because it performs repetitive and regular movements and operations in a regularized ridge area. Therefore, we studied a method that can control the steering so that it does not deviate from the path or invade the side ridge while following the center of the ridge being worked. The purpose of this study is to increase the work efficiency and convenience of the self-propelled onion harvester used in field farming.