The invention discloses a detection device and detection method for the ultra-long anchor cable hole forming quality in a karst area. The detection device is composed of an auxiliary detection device,an information acquisition device and a data processing device. The auxiliary detection device consists of a casing pipe, a casing pipe head, a fixed pulley and a rope; and the casing pipe is arranged in an anchor cable hole. The information acquisition device includes a clinometer and a tester; and the clinometer is arranged in the casing pipe. One end of the rope is fixedly connected with the clinometer and the other end goes around the fixed pulley and extends out of the casing pipe. A signal output terminal of a clinometer sensor of the clinometer is connected with a signal output terminal of the tester; and a signal input terminal of the data processing device is connected with a data output terminal of the tester. In addition, according to the detection method, the detection deviceis used for detecting the anchor cable hole forming quality. The detection device has advantages of simple structure, convenient assembling, and low detection cost; and more importantly, the signal transmission is carried out by a cable with high stability; and a problem that the transmitted signal is easy to lose is solved.