The optimal synthesis temperature of BiFeO3 is found. The cube BiFeO3 powders have a hexagonal perovskite structure with a space group R3c, while the sphere-like BiFeO3 powders have a rhombohedral structure with a space group R3m. The growth mechanism of crystallization–dissolution–crystallization has been summarized and verified. The effect of the reaction time on the particle size in hydrothermal synthetic experiment is studied. The magnetic properties of samples prepared under different alkali concentration have been measured by vibrating sample magnetometer. It is indicated that the samples with different morphologies exhibit different magnetic properties. A reasonable explanation for this phenomenon has been given in this paper.