Ettringite is one of the key hydration products of cementitious materials such as sulphoaluminate cement, common Portland cement and other clinker-free cement. Its crystal structure consists of a central column and grooves parallel to the central column. The hexagonal groove structure is around the central column and sulfate and water molecules connect in the grooves by a network of hydrogen bonds that keep the ettringite structure. In the hydration reaction of cementitious materials, ettringite crystals are easily affected by external factors. Among them, external factors such as supersaturation of reactant ions, temperature, water reducing agents, chloride ions and seed crystal often change the number of water molecules and hydrogen bonds of ettringite crystal structure, which in turn changes the stability of crystal structure as well as morphology. In addition, in the process of synthesizing ettringite crystal, the stirring paddle type and rotational speed also affect the crystal structure and morphology of ettringite, resulting in cognitive inconsistency. Based on a systematic review of the crystal structure of ettringite, the influences of various external factors on its structure and morphology in detail were summarized, various research methods were introduced, and some research suggestions on the crystal formation and morphology of ettringite were proposed.