Nonsuicidal self-injury (NSSI) is a serious risk behavior in adolescents and is a high risk factor for suicide, while negative emotions can lead to increased NSSI behaviors. In this study, we investigated the altered behavioral performance and neural reactivity of adolescents with NSSI by using a two-choice oddball paradigm when exposed to negative emotional stimuli, and analyzed the brain lateralization effect. Our data indicated that adolescents with NSSI exhibit more pronounced N250, P300, and LPP components during negative emotional face stimulation, as evidenced by a smaller N250 wave amplitude, larger P300 wave amplitude, steeper LPP waveform, and faster fallback baseline; and the presence of brain lateralization responses in both the N250 component and the LPP component. These results suggested that adolescents with NSSI showed significant alterations in cognitive EEG components associated with emotional processing during negative emotional face stimulation, particularly in EEG components representing inhibitory control, and there was a lateralization effect on emotional processing in the brain, with different processing stages and different dominance of the left and right brain.