China's lotus root industry holds a dominant position in the international market. Given that the rigid chassis of traditional agricultural machinery fails to meet the requirements for stability, trafficability, and adaptability, this study designed a variable triangular track chassis to improve the passability and stability of the harvester in soft and high water content lotus root fields. By analyzing the working conditions of the lotus root field and the force characteristics of the chassis, key parameters such as ground contact pressure of the track, traction force, and power were determined. The overall structure was optimized by using modular design and lightweight aluminum alloy material (ZL303). A three-dimensional model was established using SolidWorks, and finite element analysis was conducted on the drive wheel, variable device, and load-bearing components based on ANSYS Workbench, including stress distribution, fatigue safety margin, and modal characteristics. The simulation results show that when the total mass is 1.1 t and the maximum speed is 15 km/h, the maximum stress of the drive wheel is 44.05 MPa, the fatigue safety factor of key components is all higher than 2.4, and the lowest natural frequency is 323.3 Hz, effectively avoiding resonance with the vibration frequency (50-300 Hz) of auxiliary equipment. In addition, by hydraulically adjusting the track tension (400-2 000 N) and the variable track gauge mechanism, the chassis has a vertical obstacle crossing ability of 300 mm and water depth adaptability of 0.4 m. The whole machine adopts redundant design and modular maintenance system, effectively solving problems such as insufficient system integration, low energy efficiency, and high manufacturing costs in existing technologies. The chassis achieves a load-to-weight ratio of 54.5% when fully loaded, with a center of gravity height controlled below 420 mm. The overturning moment safety factor meets the requirements of GB/T19930-2005 standard, and it reserves 3 sets of power output interfaces and 4 standardized mounting bases, supporting rapid replacement of multi-functional agricultural operation devices, providing a reliable platform for the development of intelligent agricultural machinery equipment.