The synergistic inhibition effect of forestry and agricultural residue of walnut green husk extract (WGHE) and the anionic surfactant of SLS on the corrosion of cold rolled steel (CRS) in 2.0 mol/L H₃PO₄ solution was studied by mass loss measurement, electrochemical technique and surface analysis methods. The results show that individual WGHE or SLS exhibits moderate inhibition capacity with the maximum inhibition efficiency of c.a. 50% for a dosage of 100 mg/L at 50 ℃. However, incorporation of WGHE with SLS can obtain better inhibitive performance, and the maximum inhibition efficiency (η_w) can reach as high as 95.3%. There is a strong synergistic inhibition effect for WGHE and SLS. The synergism parameter increases with the increase of temperature in general. WGHE/SLS can more efficiently retard both cathodic and anodic reactions simultaneously. Nyquist spectrum exhibits a depressed capacitive loop, and the charge transfer resistance follows the order: WGHE/SLS＞WGHE＞SLS. SEM and AFM micrographs confirm that WGHE/SLS can efficiently alleviate the corrosion degree of steel surface in phosphoric acid media. There is a synergism between SLS with any one of the major components such as rutin, quercetin and 1-methylnaphoqinone in WGHE respectively, but their synergistic inhibition is all below that of the complex WGHE/SLS.