Sleep is important for our physical and mental health. Over the past decade, researchers have begun to focus on the impact of sleep loss on social interaction. The current article systematically reviews these studies and points out directions for further investigation. In terms of social emotion, interpersonal interaction involves a variety of prosocial and antisocial emotions, such as empathy and irritability/anger. Both correlational and experimental studies have found that emotional and cognitive empathy decrease with sleep loss, whereas irritability/anger increases with sleep loss. In terms of social behavior, interpersonal interaction refers to two, opposite types of behaviors. One is prosocial behaviors, which decrease with insufficient sleep. Specifically, sleep-deprived individuals are more selfish, distrustful of others, prone to betray others’ trust, easily discontented with money sharing proposals, and being lonelier and less drawn into social interaction. The other is aggressive behavior, which has been reported by many studies to exhibit a positive correlation with sleep loss. That is, the poorer the sleep, the more or stronger the aggressive behavior. However, evidence from several experimental studies was mixed. According to a dual-process theory, the diminished functional connectivity between emotional and cognitive systems may account for the changes after sleep loss. Such neurocognitive mechanisms act on social emotion in two ways: in regards to the top-down process, the inhibitory control of emotion from the cognitive system would be weakened, resulting in a saturated and flattened response to emotional stimuli. This explains why sleep-deprived people are more irritable and angrier at negative stimulation. In regards to the bottom-up process, cognitive system would fail to integrate information from the emotional system into higher-level cognitive judgement and decision-making, which means that although reactions from emotional system to stimulation are intensified, without cognitive integration, advanced cognitive functions such as emotion discrimination, internal mapping of one’s own affective state, and the ability to simulate the feelings of others, would be blunted. As a result, both emotional and cognitive empathy are disrupted after sleep loss. As for social behavior, the diminished functional connectivity between emotional and cognitive systems, specifically the disrupted bottom-up integration, may impair the motivational influence of social emotion on social behavior, leading to an indirect impact on social behavior after sleep loss. At the same time, the inhibitory cognitive control over behavior would also be weakened after sleep loss, resulting in a direct impact. Under the combined influence, although the motivation effect of anger/irritability on aggressive behavior may be diminished, enhanced irritability/anger and disrupted cognitive inhibition for behavior after sleep loss jointly increase aggressive behavior with insufficient sleep; moreover, the impaired role of empathy in facilitating prosocial behavior, blunted empathy, and deficits in cognitive control over prosocial behavior jointly decrease prosocial behavior after sleep loss. Further studies should investigate the effect of sleep deprivation on high-level social emotions such guilt and gratitude and the motivational influence of social emotion on social behavior via sleep restriction, which has high ecological validity.