Research has suggested a contradictory effect between detachment and reinterpretation, two distinct tactics of cognitive reappraisal, in the regulation of negative emotion. The reasons for this contradictory effect remain unclear. The present study explored the differences between these tactics in terms of potential early processes and neural mechanisms, comparing psychophysiological differences using event-related potentials (ERPs) in the regulation of negative emotion. Thirty college students were required to perform an emotion regulation task, in which they naturally viewed or applied a given emotion regulation strategy towards negative pictures. The results demonstrated that both tactics reduced emotional experiences (decrease of arousal and increase of valence). Reinterpretation was associated with reductions in the late positive potential (LPP) in the late time window, while detachment was not. Detachment showed a lower amplitude in the N1 and N2 ERP components and a higher P2 amplitude than reinterpretation. The differences in early ERP components (N1, N2, and P2) predicted the reduction of LPP amplitude. These findings reveal the differential effects of these tactics on emotional experience and neural responses and highlight the significance of early processes on emotion across the time course of cognitive reappraisal.