The invention relates to a hole grinding method of a deep hole drilling and boring machine. A first abrasive cloth strip the same as a boring head wood key groove in size is arranged on the bottom layer of the wood key groove, a second abrasive cloth strip with the length two times that of the first abrasive cloth strip is placed on the wood key groove, then a wood key is placed to be subject to beating for compression and compaction, and three wood key grooves in the other positions are operated according to the steps. A machine tool is started, the wood keys pass through a hole opening of a shaft system, and the hole opening of the shaft system grinds the wood keys until the outer diameter of the wood keys is equal to the diameter of an inner hole; the wood keys are taken down to be saw into high wood keys and low wood keys; the high wood keys are long; the high wood keys are wrapped with second abrasive cloth; the high wood keys and the low wood keys are placed into the wood key grooves, and installation of the other wood key grooves is completed; and a machine tool main shaft is started, workpieces rotate, cutting fluid is supplied, and the high wood keys and the low wood keys swell. The machine tool is started for feeding, and the second abrasive cloth wrapping the high wood keys grinds the wall face. Through the adoption of the hole grinding method, the contact area between the abrasive cloth strips and the inner surfaces of the workpieces is large, the ground faces are free of surface vibration lines, cost is low, the grinding production efficiency is high, operation is easy and convenient, the inner hole surface quality is good, and the grinding surface roughness can reach Ra1.6-Ra3.2.