In this paper, the food quick-freezing technology, the shape of ice crystal at different freezing rates and methods for observing ice crystals are described. The research progress of pressure-assisted freezing, electrostatic-assisted freezing and magnetic-assisted freezing in recent years is reviewed. The direct method can directly observe the ice crystal formed during the freezing process. The indirect method analyzes the ice crystal characteristics by observing the gap left by the ice crystal in the food after freezing. Pressure-assisted freezing can improve the super-cooling degree. When the pressure is released, the ice crystals formed by instantaneous freezing are fine and evenly distributed. Electrostatic-assisted freezing reduces the nucleation temperature and promotes the formation of smaller ice crystals. Magnetic-assisted freezing can enhance the hydrogen bond and inhibit the formation of ice crystals. These assisted freezing methods are beneficial to improve the quality of frozen food and have good application prospects.