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Subduction polarity reversal, an induced subduction initiation (SI), may occur frequently in geological history as exemplified by Solomon subduction zone. However, the mechanism and dynamics of polarity reversal remain poorly understood. Here we use 2D thermomechanical numerical models to investigate the dynamics of subduction polarity reversal during oceanic plateau accretion. Model results show that larger and lighter oceanic plateaus favor subduction polarity reversal, which is manifested by the formation of the Solomon subduction zone after the large Ontong Java Plateau collided with the former Melanesian (Manus–North Solomon–Vitiaz) trench. We analyze the stress state during the transient SI process and find that rapid extension of the oceanic plateau is concomitant with subduction polarity reversal, thus questioning the use of extensional structures as geological criteria for spontaneous SI.