An underground longwall mining method includes drilling a main shaft and an auxiliary shaft from a ground to a coal bed and exploiting in the coal bed first and second connection laneways. The first connection laneway is in communication with the main shaft, and the second connection laneway is in communication with the auxiliary shaft. The method further includes communicating the first and second connection laneways, and using a communication part between the first connection laneway and the second connection laneway as a first open-off cut; and by using a direction of the first open-off cut further away from the connecting line connecting the main shaft and the auxiliary shaft as a first direction, and exploiting by cutting a coal wall in the first direction using a coal mining machine.