Distinctive thermal-induced prismatic-type face-centered cubic zirconium phases (named gamma phase) were firstly reported in pure zirconium. Atomic insight was provided into the alpha/gamma interface and structure of interfacial misfit dislocations. Furthermore, we proposed the formation mechanism of this gamma phase. Our results revealed that the semi-coherent interface contributes to periodic extra half-plane on the gamma side and the volume expansion is 19.8% due to the alpha -> gamma phase transformation. More importantly, the alpha -> gamma phase transformation involved expansion and shuffle displacement.