The invention belongs to the field of mechanical automation and discloses a double-tool-rest reliability test device and a method for detecting the rotation precision of double tool rests. The double-tool-rest reliability test device comprises a base supporting portion, a cutting force loading device, an automatic control device, a numerical control tool rest portion and a detecting device portion mounted on the numerical control tool rest portion. The cutting force loading device comprises a loading hydraulic cylinder, a loading force rod, a double-fork loading head, an auxiliary force loading device, a rotary locking mechanism and a hydraulic cylinder supporting structure. The automatic control device comprises an X-direction moving platform, an X-direction moving platform motor, XY guide tracks and optical-electricity encoders. The numerical control tool rest portion is mounted on the XY guide tracks. By means of the double-tool-rest reliability test device and the method for detecting the rotation precision of the double tool rests, the cutting force of the actual working condition can be accurately simulated, moreover, the two numerical control tool rests can be loaded at the same time, the test efficiency is improved, the production time is shortened, and the production cost is reduced. By means of the method, an obtained detection result is closer to the rotation precision of the tool rests during actual production, and the research value of the detection result obtained through the method is higher than that of the detection result obtained during idling of the tool rests.