The invention discloses a motor bearing assembling clearance detecting method. The method comprises steps as follows: S101, a feeler gauge is inserted in radial clearance between a bearing block and an isolating sleeve, the feeler gauge is taken out and a bearing outer cover is put on a bearing after the radial clearance is equally spaced in the circumferential direction through adjustment and meets the size requirements of the feeler gauge; S102, a plurality of clearance detecting pieces are inserted into the radial clearance through process detection holes in the bearing outer cover, fastening bolts symmetrically arranged on the bearing outer cover are screwed tightly, and the clearance detecting pieces are pulled; S103, whether the radial clearance meets the size requirement of the clearance detecting pieces is judged, if yes, the step S104 is performed, and otherwise, the step S105 is performed; S104, the clearance detecting pieces are taken out, the feeler gauge is inserted into the radial clearance, and the step S106 is performed; S105, the bearing outer cover is taken down, and the step S101 is performed again; S106, whether the radial clearance is uniformly spaced in the circumferential direction is judged, if yes, operation ends, and otherwise, the step S107 is performed; S107, the bearing outer cover is taken down, and the step S101 is performed again. The invention further discloses a motor bearing assembling clearance detecting device. The stability of clearance adjustment of the bearing is improved.