The invention provides a GIS combined switch dust-free assembling workshop and assembling method, belonging to the technical field of electric power systems. The assembling workshop includes an air shower channel and an operating room, the air shower channel is assembled between the external environment and the operating room, and the operating room includes a vibration isolation system and an operating system integrating cleaning, vacuum-pumping, and gas filing into one body. The assembling method includes that an operator enters in the operating room through the air shower channel from the outside by carrying the device, puts the device to the vibration isolation system, and then cleans the device, performs exhausting and inflation on a GIS combined switch for multiple times, vacuum-pumps the GIS combined switch by performing the exhausting operation for the last time, and at the end, inflates the GIS combined switch with sulfur hexafluoride gases. The GIS combined switch dust-free assembling workshop and assembling method can effectively improve the purity of sulfur hexafluoride and further improve the performances of the GIS combined switch.