The lateral photovoltaic effect (LPE) has been widely employed in optoelectronic devices for its high sensitivity and broadband responsivity. Typically, the physical mechanism of LPE is based on Schottky junction or PN junction. In this article, we present experimental evidence for multiple lateral photovoltaic mechanisms in Ag/p-Si structures and demonstrate the dominant mechanism of LPE can be converted from surface states to the Schottky barrier or localized surface plasmon resonances (LSPRs) by tuning the Ag thickness. We believe this experimental result extends the knowledge into the underlying mechanisms of LPE and presents a wide range of possibilities for the further development of LPE-based photodetectors.