The invention provides a heat balance test method and device for a power battery system. According to the method, the performance of a power battery system under high-temperature test of a vehicle issimulated in a high-temperature environment to find the optimal discharge power corresponding to different working conditions. The power battery system can meet the requirement for the heat balance performance under various different working conditions. The situation in which there is a need to redesign the heat balance performance of the power battery system will not occur easily. Normal operation of the power battery system is ensured. Therefore, an optimal heat balance control strategy for the power battery system can be given before vehicle test.