A controlling method is provided for preventing a solid state drive from being operated at a high temperature. The solid state drive includes a controlling circuit, a temperature detecting circuit and a plurality of dies. The dies are divided into n groups and accessed by the controlling circuit through n IO buses. The controlling circuit is in communication with the temperature detecting circuit for detecting a temperature of the solid state drive. The controlling method includes the following steps. Firstly, a judging step is performed to judge whether the temperature of the solid state drive is higher than a predetermined temperature. If the temperature of the solid state drive is higher than the predetermined temperature, the frequencies of n clock signals in the n IO buses are decreased.