Polymorphism has attracted significant attention in the area of pharmaceutical chemistry and materials chemistry. For energetic materials, polymorphism may affect their physical performances such as energy, sensitivity, thermal stability, etc. 4,4′,5,5′-Tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI) exhibits high density (d: 1.93 g cm-3), superior detonation performance (D: 9063 m s-1) and comprehensive sensitivity (IS: 15 J), suggesting it is a nonsensitive-high-energy material (NSHEM) compared with HMX as a sensitive-high-energy material (SHEM). In this work, a new polymorph of DATNBI was discovered for the first time. To elucidate its phase transformation behavior and morphology-performance relationship, single X-ray diffraction (SXRD), variable temperature powder X-ray diffraction (VT-PXRD), Raman spectroscopy, differential scanning calorimetry-thermal gravity (DSC-TG), and scanning electron microscopy (SEM) were characterized thoroughly. Solvation and temperature effects on the polymorph formation of DATNBI were also investigated.