A device for fixing a rock sample, including: a lower clamp and an upper clamp; the lower clamp including a lower connector connected to a loading base at a bottom of a testing machine, a lower end cap for fixing samples, a lower chain connecting the lower connector and the lower end cap, a first spiral spring, a first central position-limit mechanism, a second central position-limit mechanism, and a first hydraulic mechanism; the upper clamp including an upper connector connected to a loading base at a top of the testing machine, an upper end cap for fixing samples, an upper chain connecting the upper connector and the upper end cap, a second spiral spring, a third central position-limit mechanism, a fourth central position-limit mechanism, and a second hydraulic mechanism.