Abstract: Multiple Fatigue Cracks problem, which includeswidespread fatigue damage problem and multiple site damage problem, iscurrently a focus of many studies. It is introduced in this paper.The objective of this research is to deal with aging structures, mainly aging airplanestructures, to establish a computing model of multiplefatigue cracks problem and a failure criteria of multiple fatiguecracks structures. This research lays down a base for assessing fatiguereliability of the aging structures.