In this study, the synthesis of zeolitic imidazole framework (ZIF-8) in water was systematically studied using 6 zinc sources (Zn(OAc)2, ZnSO4, Zn(NO3)2, ZnCl2, ZnBr2, ZnI2), respectively, under different conditions at room temperature without using any additives. It was found that Zn(OAc)2 is the best precursor and the resultant ZIF-8 particles have the best quality with rhombic dodecahedron morphology. The concentration of 2-methylimidazole (Hmim), molar ratio Hmim/Zn and water content all have significant impacts on the morphology, particle size, and crystallinity of ZIF-8. Further result analysis reveals that 3 key reactions are involved in the ZIF-8 formation which needs five steps in ZIF-8 structural evolution. This study provides a deep understanding of the crystallization process of ZIF-8 particles in a water-based system.