The invention belongs to the field of rock mechanics, and provides a device and method for preparing rock test pieces of different sizes and joint inclination angles. The device for preparing rock test pieces of different sizes and joint inclination angles comprises a base, a rotary disk and a to-be-cut complete rock test piece fixing assembly, wherein the to-be-cut complete rock test piece fixingassembly comprises a T-shaped guide rail, a test piece end face fixing assembly and a test piece side face fixing assembly; the rotary disk is hinged to the base through a spherical hinge; the T-shaped guide rail is provided with an arc-shaped groove, and carved with a graduated scale; the T-shaped guide rail is fixedly connected to the rotary disk; the test piece end face fixing assembly is in aslip connection with the T-shaped guide rail; and the test piece side face fixing assembly is fixedly connected with the rotary disk through a fixing plate. Through adoption of the device and methoddisclosed by the invention, rock samples of different sizes and joint inclination angles can be prepared by adjusting device assemblies, so that the preparation accuracy of original rock samples of different sizes and joint inclination angles is improved. The device has the advantages of unique structure, reasonable structure, convenience in operation, durability and the like.