A battery temperature adjusting device used for an on-line monitoring device of a transmission line relates to a battery temperature adjusting technology for an on-line monitoring device of a transmission line to solve the problem that a battery of an on-line monitoring device is low in stability because an environment where the battery stays is affected by temperature. An inner sleeve of the battery temperature adjusting device has the same shape as a double-layer vacuum glass tube. A rotary shaft is fixed on the inner wall of the inner sleeve. The rotary shaft passes through a rotary separation plate horizontally, and rotation is conducted by taking the rotary shaft as the axis so that the opening of the double-layer vacuum glass tube is adjusted. A temperature sensing coil spring is rigidly connected with the rotary shaft and the rotary separation plate. A heat-insulating plate is arranged horizontally inside the double-layer vacuum glass tube, the side wall of the heat-insulating plate is in close contact with the double-layer vacuum glass tube, a gap exists between the heat-insulating plate and the closed end of the double-layer vacuum glass tube, and a gap exists between theheat-insulating plate and an adjusting cover. A battery chamber is arranged on the lower surface of the heat-insulating plate, and the battery chamber is used for accommodating a battery. The beneficial effect of the device is that an environment where the battery stays is improved.