Single-sided deafness (SSD) refers to severe to profound sensorineural hearing loss on one side (average pure-tone hearing threshold≥70 dB HL at 0.5, 1, 2, and 4kHz) while the opposite side maintains normal hearing or mild hearing loss (30 dB HL). Asymmetrical hearing loss (AHL) refers to severe to profound sensorineural hearing loss in the bad ear (average pure-tone hearing threshold≥70 dB HL at 0.5, 1, 2, and 4kHz) and mild to moderate hearing loss in the contralateral ear. Moderate hearing loss (30≤mean pure-tone hearing threshold≤55dBHL). It is generally acknowledged that SSD is a particular clinical manifestation of AHL. The number of people who have hearing loss accounts for 5.3% of the total population, with children for 9%. According to the Second National Sampling Survey on Disabled Persons, China has 27.8 million people with hearing disabilities. The incidence of SSD adults in the United States is 7.2%, with 60,000 new cases per year, compared with 7,500 new patients with SSD annually in the UK. The incidence of SSD in neonates is 0.04%-0.34%, and it ranges from 0.1% to 0.5% in children and adolescents. The etiology of congenital SSD is primarily unknown, which is related to genes. Among the causes of acquired SSD, sudden deafness is the most common. Other causes include head trauma, Meniere's disease, labyrinthitis, unilateral acoustic neuroma, middle ear surgery, ototoxic drug exposure, Virus infection, noise-induced deafness, senile deafness, etc. SSD and AHL impede intellectual development and speech development in children and adolescents, which is associated with the side of hearing loss. For example, children with right-sided hearing loss have relatively poor language learning, logical thinking, and divergent thinking. In contrast, children with left-sided hearing loss have weaker analytical, comprehensive and visual memory abilities and relatively poor spatial imagination and visual-motor coordination. In addition, the lack of long-term monaural listening and sound source localization makes SSD children require excessive concentration, which is prone to fatigue and behavioral problems, and their academic performance is lower than that of normal children.