Abstract: Ca_0.925Sm_0.05Cu_3-yMg_yTi₄O₁₂ (y=0, 0.05, 0.10, 0.15, 0.20, molar fraction/%) thin films were prepared on Si(100) substrate by sol-gel method. Effects of Mg doping amount on phase composition, micromorphology, dielectric property and pressure-sensitive performance of the film were studied. The results show that the thin films with different doping amounts of Mg were mainly composed of polycrystalline CaCu₃Ti₄O₁₂ phase and a small amount of SiC and CaTiO₃ phases. With increasing Mg doping amount, the grain size and relative dielectric constant of the film increased. After doping with 0.10mol% Mg, the film had the highest density and the smallest dielectric loss at relatively low frequencies. The thin films with different doping amounts of Mg exhibited a nonlinear relationship between current density and electric field strength. When the film was doped with 0.10mol% Mg, its nonlinear coefficient was the largest, and leakage current was relatively small.