For the difficult problem of detecting large curvature path of nature image processing, a double tangent-line detection algorithm for turning radius based on rotation and projection line detection arithmetic was put forward. On the base of kinematics of simplified two-wheel vehicle model, an intelligent controller was constructed for the vision navigation test platform of combine harvester. The controller could select different control mode according to the different path (including straight path and curve path). The tests on road with tag line and in wheat field with curvature cut boundary showed that the double tangent-line detection algorithm was valid to detect turning radius and the system could trace the curvature path whose radius was greater than 10m. During the normal working speed, the maximum error of tracing large curvature path on road was 0.19m and in field the change of harvesting width was within 0.29m. 