This study investigates the through-cracking mechanism of the outer ring of an MT-1 double-row spherical roller bearing for coal mine belt conveyor pulleys. Macroscopic observation, SEM fractography, chemical analysis, hardness testing, metallographic examination and inclusion assessment were performed. A large fatigue spalling zone and through-crack formed on the 5–7 o’clock section of the outer ring raceway, while transient impact induced edge chipping on the inner ring flange. Microstructural results show crack initiation at the base of a spalling pit, with fracture surfaces exhibiting fan-shaped fatigue propagation, quasi-cleavage and intergranular brittle fracture. Pre-existing surface damage was identified at the crack origin. High-magnification SEM revealed early wear marks and butterfly white etching areas (WEAs) around subsurface inclusions under high contact stress, acting as microcrack nucleation sites. Such initial defects, likely from improper transport or sudden overload, reduce bearing steel fatigue resistance and accelerate crack growth. Material characterization confirms the bearing meets standard requirements for composition, hardness gradient, martensite–carbide microstructure and inclusion rating, excluding raw material and heat-treatment defects. Underground service conditions including long-term eccentric loading, contaminant ingress, lubrication failure and cyclic vibration concentrate stress around inclusions, triggering subsurface fatigue, progressive spalling and eventual through-cracking. Outer ring fracture disrupts load distribution, leading to secondary chipping of the inner ring flange. This work provides theoretical support for lubrication maintenance, assembly alignment and seal optimization, improving the reliability of heavy-duty spherical roller bearings in harsh mining environments.