The invention provides a computing method for the heat management available power, a heat management controller and a heat management system. The heat management system comprises the heat management controller, the heat management controller uses the computing method to compute the heat management available power under the limiting working condition, computing of the drive available power is comprehensively considered while the heat management available power is computed through the computing method, and the heat management available power adopts a first-order low-pass filtering algorithm, and the size of the filtering parameters depends on that of the drive demanded power variation rate; and the drive available power limit coefficient adopts a PI algorithm, and the parameter P and the parameter I vary from the difference value of the drive available power and the actual drive power. By adoption of the computing method provided by the invention, under the limiting working condition, on the basis of the condition that the vehicle security requirement is met, driveability can be ensured to a largest extent, and power battery over discharge is avoided.