Abstract：A team of transparent specimens using a type of casting resin are employed，which has brittle fracture properties of rock-like material under frozen environment. The primary flaws in samples are made of three thin aluminum films. The propagation and coalescence process of three-dimensional(3D) flaw sets were observed. The experimental results show that wrapping wing cracks individually initiate and grow from every pre-existing flaw end at the beginning of fractures. Then the interaction roles between the flaws gradually become stronger and stronger，and principally，the secondary cracks are induced to extend towards the direction opposite to wing crack. This type of crack is so called wrapping anti-wing crack(against wrapping wing crack). The whole specimens will be broken off by the coalescence fracture of wrapping wing and anti-wing cracks. Furthermore，the distribution type of 3D flaws will greatly affect some parameters of growth and coalescence of 3D cracks. Especially，the initial growth angle of crack will change by about 10°. Finally，the primary fractured pattern and mechanism of 3D flaw sets are discussed in this paper.
