A statistical theory of delayed fracture in a wide range of stress (1》(ασ)/(Kt)》1) has been proposed. The fundamental idea is that microcrack stochastically evolves based on the atomic bond mechanism leading to fracture. The microcack evolution equation is given. The microcrack distribution function, fracture probability, reliability, the statistical distribution function of fracture strength and fracture life and their statistical average value are derived.