Humic acids are natural organic substances that are produced as a result of biological and geochemical reactions in environment and are known as one of the main precursors of disinfectant by-products (DBPs). New types of PAC/LaFeO3/Cu nanocomposites are synthesized by sol gel method for photocatalytic degradation of humic acid under visible light irradiation. The physicochemical functions of PAC/LaFeO3/Cu nanocomposites were characterized using BET, TEM, UV–vis DRS, XRD, and PL spectroscopy. Results emphasize that, free hydroxyl radical (•OH) attack to HAs molecules, decompose and oxidize the molecules to CO2, H2O, and other small components. Central composite design (CCD) was applied to optimize HAs removal based on response surface methodology (RSM) with four experimental parameters such as pH (X1, 3–11), catalyst dosage (X2, 100–1300 mgL−1), contact time (X3, 15–55 min), and HAs concentration (X4, 2–10 mgL−1). Removal efficiency of 95.5% for HAs has been obtained under optimal conditions with 36.20 min (exposure time), 5.33 mgL−1 HAs concentration, 715.74 mgL−1 PAC/LaFeO3/Cu dosage, and 4.20 pH. The HAs degradation efficiency was significantly affected by the initial dye concentration and the pH values. The significance of the polynomial model was validated by analysis of variance (ANOVA). This work seeks to illustrate new knowledge for usage of nanocomposites photocatalyst as an inexpensive, environmentally friendly, economical, and effectual material for drinking water supplies treatment processes. However, the PAC/LaFeO3/Cu nanocomposites showed excellent removal performances for HAs.