Abstract: Hg(II) accumulation in organisms can cause serious threats to human health and ecology. Therefore, it is crucial to sensitively, rapidly, and accurately detect Hg (II) under different conditions. To construct an effective electrochemical sensor for Hg(II), phytic acid doped carbon nanotube network (PACNTnet) and popcorn-like copper nanoparticles (popCu) were electrodeposited on the surface of screen-printed carbon electrodes (SPCE) through cyclic voltammetry and the potentiostatic method. A large number of binding sites for Hg(II) were generated on PACNTnet with oxygen-containing functional groups and phosphates being predominant. The sensing signal was amplified by the synergistic effect of Cu(II) and Hg(II). A sensitivity of 5.51 μA/(μg·L⁻¹) was achieved with a linear range of 0.02—2 μg/L, and a detection limit of 0.012 μg/L was determined. Furthermore, a satisfactory recovery rate of Hg(II) was obtained in rice and tea samples. Using ICP-MS as a reference method, the accuracy of the as-fabricated sensor was corroborated. The results indicated the potential of popCu/PACNTnet/SPCE for Hg(II) detection in real-world samples.