The invention relates to a ball bearing radial internal clearance automatic detecting device. The ball bearing radial internal clearance automatic detecting device solves the problems that existing dial indicator measurement is achieved through manpower, so that the labor intensity of workers is large, the workers are prone to feeling tired after long-time work, and measurement errors can further occur. The ball bearing radial internal clearance automatic detecting device comprises a bearing positioning mechanism, a material rejecting grading mechanism, an inner ring clamping mechanism, an outer ring ejection mechanism and a measuring mechanism; the bearing positioning mechanism comprises a bearing limiting material channel and a limiting mechanism; the inner ring clamping mechanism comprises a bearing inner ring clamping mechanism and a bearing suspension mechanism; the outer ring ejection mechanism is arranged below the bearing limiting material channel, and a material rejecting opening is formed in a material channel base plate; the material rejecting grading mechanism is arranged at the position of the material rejecting opening. A bearing inner ring is automatically clamped through an automatic clamping mechanism to enable a bearing to be suspended, a bearing outer ring is upwards ejected through an automatic ejection mechanism, final data are measured through a measurement instrument, the two data are calculated and processed by a processor to generate a radial internal clearance of the bearing, the automatic degree is high, and the labor intensity of the workers is reduced.