Due to the shortcomings of ergonomics and comfort in the design of tractor cabs, the mathematical model of each joint of the human body was established by theoretical calculation. The model was based on a definition of the angle and length of each joint of the human body in GB/T 21935—2008 standard, and the recommendation of GB/T 6235—2004 on the seat marking points position. Based on the simulation analysis of human manipulation based on RAMSIS software, a three-dimensional model of human manipulation comfort zone on both sides of the driver's seat was constructed based on the optimized range of human manipulation comfort zone and accessibility zone specified in GB/T 21935—2008 standard. Combined with RAMSIS software, the existing tractor cab internal control components were optimized. The included angle between the foot accelerator pedal surface and the floor surface was adjusted from 45°to 35°. The overall position of the foot accelerator was shifted outward by 25mm, and the width of the brake pedal surface was reduced by 40mm. At the same time, the structure at the 265mm distance from the ground of the main gear lever was adjusted outward by 20mm, and the initial position of the hand brake was raised by 45mm. Experiments were carried out on the optimized prototype, and the control force and stroke of each component were measured to verify the correctness of the proposed three-dimensional model of the human operation comfort zone. During the present study, a mathematical model of the comfort zone and the arrangement position of the control components was provided for the ergonomic design of the tractor cab. The research result could provide a reference for the tractor cab design. Also, it would expand the application of ergonomics in the field of tractor design and improve the driving comfort of tractors.