The invention provides a hard disk fixing device. The hard disk fixing device comprises a fixing frame; the fixing frame comprises an end wall and a first fixing wall and a second fixing wall which are vertically extended from both ends of the end wall along the same direction; an accommodating space capable of accommodating a first hard disk is formed among the end wall and the first fixing walland the second fixing wall; the first fixing wall and the second fixing wall are fixed on both sides of the first hard disk respectively; the hard disk fixing device also comprises a support arm pivotally arranged on the fixing frame, the support arm is provided with a fixing part and can rotate between a first position and a second position, when the support arm is at the first position, the fixing part is in the accommodating space and parallel to the first fixing wall and the second fixing wall respectively and keeps a distance away from the first fixing wall and the second fixing wall, and the fixing part and the second fixing wall can be fixed on both sides of a second hard disk respectively; and when the support arm is at the second position, the fixing part is on the outer side of the accommodating space, and the hard disk fixing device can fix the first hard disk. By using the hard disk fixing device, the hard disks can be conveniently changed.