The invention discloses a bolt heating hole inner wall crack detecting device and method. A detecting seat is arranged at the front end of a detecting rod, the outer diameter of the detecting seat is matched with the inner diameter of a central heating hole of a bolt, the front end of the detecting seat is matched with the blend end of the central heating hole of the bolt in shape, an arc-shaped chamfer is arranged on the edge of the front end of the detecting seat, a first eddy probe arranged in a bilaterally symmetric mode is installed at the front end of the detecting seat in an embedded mode, a second eddy probe arranged in a bilaterally symmetric mode is embedded into the arc-shaped chamfer, and the first eddy probe and the second eddy probe are located on the same straight line and used for detecting cracks at the blind end of the central heating hole of the bolt. Four or eight third eddy probes are installed on the outer wall of the front end of the detecting seat in an embedded mode and used for detecting the cracks of the inner wall of the central heating hole of the bolt. The bolt heating hole inner wall crack detecting device performs detection when the bolt temperature is reduced to be below 300 DEG C, is short in period and high in detection accuracy and suitable for various bolts with central heating holes which are blind holes or through holes and has a good application prospect.