Fatigue crack propagation behaviors and crack length distribution on the surfaces of smooth specimens under completely reversed bending were investigated for a ferritized spheroidal graphite cast iron and silicon steel plate. The variations of fatigue crack propagation and the crack density on the ferritized spheroidal graphite cast iron were much higher than those on the silicon steel plate because of the presence of many graphite nodules. The cumulative probability of crack length distribution in both ferritized spheroidal graphite cast iron and silicon steel plate could be presented by Weibull distributions with a function of crack length. Moreover, the cumulative probability of crack length distribution showed a knee on the ferritized spheroidal graphite cast iron in the early stage of fatigue life. It became clear that the crack length on this knee and a minimum coalescence crack length were almost equal numerically.