Computer system and controlling method for hard disk

A computer system and a controlling method for a hard disk are provided. The computer system includes a case, a hard disk, a pressure sensor and a controller. The hard disk is disposed in the case and includes a platter and head, which is used to access the platter in an access range. The pressure sensor is disposed between the hard disk and the case, and is configured to obtain a pressure value. The controller is coupled to the pressure sensor and the hard disk, and is configured to determine if the pressure value is larger than or equal to a threshold. If the pressure value is larger than or equal to the threshold, the controller issues a command to the hard disk, such that the head leaves the access range. Accordingly, the hard disk is prevented from being damaged.