Abstract: Green energy and clean vehicles have triggered the power improvement of electric vehicles, as most agricultural machine equipment are becoming much more electric. Large-scale battery and high current discharge have gradually served as a power supply, leading to the formation of much heat during rapid charge and discharge cycles at high current levels. Therefore, it is inevitable to cause the thermal accumulation in batteries, thereby to exceed the optimal operating temperature range, particularly in agricultural vehicles with the more complex working conditions and the compact layout of battery packs. An appropriate strategy of thermal management is necessary to control the battery temperature within a reasonable temperature range. In this study, a thermal management system of power battery was presented with cooling or heating functions, using the techniques of phase-change heat transfer and pump-free circulation. Taking ternary lithium batteries as the research objects, the two-way working modes of thermal management system were tested under cooling or heating conditions, thereby to investigate the influence of inclination angle on heat dissipation and temperature uniformity. In the case of cooling, the cooling capacities of two thermal management systems were studied under natural and forced convection cooling conditions, when the initial temperature of battery box was set as 40 ℃, 50 ℃, 60 ℃ and 70 ℃. In the case of heating, the heating capacities of two thermal management systems were also studied, together with the initial temperature of different batteries, and the heat exchange uniformity of two thermal management systems. The results showed that the proposed system can realize the switching operation management of cooling and heating in two-way modes, based on high or low temperatures. Specifically, the switch of thermal management can be implemented by controlling the opening and closing of the valve at the preset temperature. Under the cooling condition, the heat dissipation capacity of heat exchanger plate with four vertical tubes was stronger than that of the single serpentine tube. Compared with natural convection, forced convection on the condenser side can increase the heat transfer power of system 1 by 10%-44.2%, and system 2 by 20%-48.6%;When the temperature of battery box was 60 ℃, the maximum temperature difference of heat exchange plate was less than 2 ℃ in the natural convection heat dissipation system, whereas less than 1 ℃ in the forced convection heat dissipation system. At an initial battery temperature of 25 ℃ and the discharge rates of 1C, 2C, and 3C, the forced convection heat dissipation at the end of discharge can reduce the average temperature of battery box by 2.1 ℃, 3.9 ℃, and 4.7 ℃, respectively. Under the heating condition, the power of battery box was consistent in many groups of experiments. The flow distribution of working fluid can be confined, considering the tilting effect of heat exchanger plate in the vehicle driving, indicating the temperature uniformity was better than that in the heating dissipation condition. The findings demonstrated that two systems of thermal management can provide better heat transfer in the complex agricultural vehicles.