The invention provides a battery module thermal management device and a method thereof. The battery module thermal management device comprises a plurality of deflectors, a driving mechanism, a temperature sensor and a controller, wherein the deflectors are located at the bottom and the side of a battery individual; the driving mechanism is connected to the deflectors and drives the deflectors to adhere to or separate from the bottom and/or the side of the battery individual; the temperature sensor is used for acquiring the temperature signal at the bottom and the side of each battery individual; the controller is connected to the temperature sensor and the driving mechanism; the temperature signal acquired by the sensor is transmitted to the controller; and the controller controls the driving mechanism in order that the deflectors adhere to or separate from the bottom and/or the side of the battery individual according to the temperature signal. The battery module thermal management device solves the temperature imbalance of the battery individual at various positions in the battery module, ensures the temperature uniformity of the battery individuals, and is simple in structure and easy to implement.