The invention discloses a calibration system and a calibration method of a partial discharge ultrahigh frequency detection device in the technical field of online detection of the partial discharge of power transformers and gas insulation combination switch devices. The calibration system comprises a standard antenna, a standard pulse source, a detection and control computer and a partial discharge ultrahigh frequency detection device to be detected, wherein the standard pulse source, the detection and control computer and the partial discharge ultrahigh frequency detection device to be detected are connected sequentially. The partial discharge ultrahigh frequency detection device to be detected comprises a sensor for collecting voltage signals. The calibration system further comprises a coaxial cavity, the coaxial cavity is composed of an outer cylinder, an inner cylinder, two outer cones and two inner cones which are coaxial, and a detection window is arranged in the middle of the outer cylinder. The invention also provides the calibration method with the calibration system. The calibration system utilizes the matched coaxial cavity to replace a small GTEM (Giagahertz Transverse Electromagnetic Cell) for the calibration of the partial discharge ultrahigh frequency detection device, and is simple in structure and easy to implement.