Abstract Homer–Wadsworth–Emmons (HWE) reaction of diethyl benzylphosphonate (DEBP, pKa=27.55) with aldehyde was performed in a solid–liquid phase-transfer catalysis (SL–PTC) system using sodium hydroxide as the solid phase. Various parameters that influenced the pseudo-first-order rate constant including stirring speed, catalysts, salt, water and temperature were investigated to explore the process of the generation and transfer of the active intermediate. A reasonable interfacial mechanism of the PTC reaction of the weakly acidic substrate was proved for the first time. HWE reactions under SL–PTC conditions showed high activity and geometric selectivity. It is anticipated that this simple and controllable synthesis method should provide a new idea for HWE reaction in chemical industry.