The present invention provides a GIS basin-type insulator dielectric loss test device and method. The GIS basin-type insulator dielectric loss test device comprises a high-voltage bridge, a high-voltage power supply, a standard capacitor and an insulator test tooling, the insulator test tooling is equipped with a tested basin-type insulator on which the dielectric loss test is to be carried out, and the above devices are connected according to the principle of the high-voltage bridge. A movable pedestal is arranged at the bottom of the insulator test tooling and is equipped with a glass cylindrical body, and the glass cylindrical body is connected with the tested basin-type insulator via a glass fiber reinforced plastic threaded rod. The GIS basin-type insulator dielectric loss test deviceof the present invention can be connected with the threaded holes uniformly distributed on the basin-type insulator via the four movable glass fiber reinforced plastic pedestals, so that the stray capacitance of a tested sample is fixed effectively. Moreover, by being equipped with the movable pedestal, the GIS basin-type insulator dielectric loss test device can satisfy the basin-type insulatorsof different sizes, and solves the technical problem that the conventional test device cannot carry out the dielectric loss test aiming at the basin-type insulators of different voltage grades and different sizes in a GIS.