Relaxor ferroelectric single crystals with perovskite (ABO3) structure possess excellent electromechanical coupling properties and are considered as the key materials of next-generation medical ultrasound transducers, high-precision piezoelectric actuators, and underwater acoustic transducers. According to the existing fundamental science and material preparation issues in relaxor ferroelectric crystals, this manuscript reviews the research progresses on the crystal growth and property optimization of relaxor ferroelectric singles in recent years. This review covers the following aspects: new crystal growth methods for enhancing the uniformity of composition and properties; new methods to improve the piezoelectric properties of relaxor ferroelectric single crystals; the control of ferroelectric domain structure to achieve high-light transmittance of relaxor ferroelectric crystals; the application of high-performance relaxor ferroelectric single crystals in the field of electro-optical technology.