A control device and method are used for adjusting the refresh rate of a memory module in a computer system. The device includes a thermo sensor and a control circuit. In the control method, the thermo sensor actively outputs a temperature change signal in response to the temperature change in the memory module when a capacitor of the memory module incurs an aggravated current leakage due to the temperature rise. Next, the control circuit adjusts the refresh rate in response to the temperature change signal and refreshes the memory module at the refresh rate.