The embodiment of the invention provides an underground temperature measurement device and method. The device is applied to a target well, and comprises a first bushing, a hollow rod and an optical fiber, wherein the hollow rod is arranged on the outer wall of the first bushing; the bottom end of the hollow rod in the vertical direction is of a wedge shape; the optical fiber is arranged in the hollow rod and is used for monitoring temperature of the target well. According to the underground temperature measurement device disclosed by the invention, the hollow rod is arranged along the first bushing, and the optical fiber penetrates into the hollow rod for temperature measurement, so that the technical problems that distributed type continuous monitoring cannot be realized for a well temperature section of the target well in the existing underground temperature measurement method and an underground temperature measurement process is easily affected by other work in the target well are solved, and the technical effect of accurately and continuously monitoring the temperature of the target well is achieved.