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In order to explore the synergistic corrosion inhibition effect of spinach extract and KI on Q235 steel in 0.5 mol/L H₂SO₄ solution，the synergistic corrosion inhibition effect and mechanism of spinach extract chlorophyll (CHL) and KI on Q235 steel in 0.5 mol/L H₂SO₄ solution were studied by means of weight loss method，electrochemical impedance spectroscopy (EIS)，potentiodynamic polarization curve，scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Results showed that when CHL (100 mg/L) and KI (50～200 mg/L) were combined in 0.5 mol/L H₂SO₄ solution，the obtained compound always showed good corrosion inhibition with a corrosion inhibition rate above 90%.And when both CHL and KI were mixed with a concentration of 100 mg/L，the synergistic effect was the best，with a corrosion inhibition rate up to 98.04%.The compound of CHL and KI was a kind of mixed corrosion inhibitor that mainly inhibited the cathode.The corrosion inhibition behavior of CHL and its complex with KI conformed to Langmuir isothermal adsorption equation，which was a spontaneous adsorption process and formed a dense protective film on the surface of Q235 steel.In 0.5 mol/L H₂SO₄ solution，CHL molecules were adsorbed on the surface of Q235 steel through physical and chemical adsorption to prevent corrosion reaction.The addition of KI could assist CHL molecules to adsorb on the surface of Q235 steel，improving the adsorption rate of CHL molecules.In this way，the corrosion rate as well as the amount of CHL and KI required for the inhibition were both reduced.Therefore，the synergistic effect of CHL and KI was enhanced and the inhibition efficiency was improved.