Abstract: Design knowledge of tractor gear box is lacking at present. Particularly, there is no systematic design flow to support the specific design for the gear box in a tractor. The lack of design knowledge and the less evaluation of performance can lead to a long development cycle of products, unstable design quality, high cost of design and manufacturing for tractor gear box. In this study, a knowledge-based rapid design method was proposed, while a rapid design system was established for tractor gear box. The system was verified by a case study. A finite element method was used to analyze the data of system design, compared with a commercial products in the same transmission scheme. Firstly, the detailed design process of tractor gear box was summarized on the extensive knowledge in this field; Secondly, design knowledge was obtained from some national standards, enterprise design specifications and theoretical books, and then the knowledge was divided into the principle class and instance class, which were expressed by production and frame representation, respectively. A knowledge base was established in the platform of SQL Server2012. A top-down design method was explored in a skeleton model. A parametric modeling was carried out in the multi-information skeleton model. A hybrid reasoning method was used based on the rule and case using MFC of Visual Studio 2015. The human-computer interaction interface and bottom reasoning mechanism of system were compiled to complete the connection with knowledge base and model base, and further to establish the rapid design system for the gear box of power shift in a tractor. The proposed system was also applied to the specific design in the gear box of power shift with a rated power of 110 kW. Finally, the rear-suspended farm tools lifting, emergency turning and one-wheel hanging were selected as the typical working conditions of the whole vehicle, while, the forward-first gear four-wheel-drive creeping and reverse-first gear four-wheel-drive creeping were selected as the typical working conditions of the transmission. A platform (Ansys workbench 18.1) was used to simulate the output model of system, where the maximum deformation was 0.450 mm, the maximum equivalent stress was 206.19 MPa, the maximum gap change was 0.007 8 mm, the maximum offset was 0.026 mm, and the first natural frequency of gear box was 405.28 Hz, indicating that excellent characteristics, including the strength, rigidity, sealing, and dynamic in the gear box. Compared with a commercial products in the same transmission scheme, the height of gear box was reduced by 28 mm, and the mass was reduced by 28.8 kg, indicating a higher material utilization. The results demonstrated that the proposed system can be used to realize the knowledge-based rapid design of tractor gear box. The finding can provide a significant reference to shorten the design cycle, while improve the design quality.