Based on the liquid-drop model, we propose and refine a local formula for the released energy of proton radioactivity (Qp). The calculated results for 44 proton emitters with 71 ≤ Z ≤ 91 are in good agreement with the experimental data. For comparison, the WS4 [Phys. Lett. B 734, 215 (2014)] and FRDM [At. Data Nucl. Data Tables 125, 1 (2019)] nuclear mass models are also employed. The root-mean-square (RMS) deviations between the experimental data and theoretical results obtained from this work, WS4, and FRDM are 0.071 MeV, 0.144 MeV, and 0.348 MeV, respectively. These results demonstrate that the present approach reproduces the experimental Qp values well in the considered region. The formula is further employed to predict the released energies for candidate proton emitters, and the predictions are broadly consistent with those of the other models.