In the ring current dynamics, various loss mechanisms contribute to the ring current decay, including the loss to the upper atmosphere through particle precipitation. This study implements the field-line curvature (FLC) scattering mechanism in a kinetic ring current model and investigates its role in precipitating ions into the ionosphere. The newly included process is solved via a diffusion equation in the model with associated pitch-angle dependent diffusion coefficients. The simulation results indicate that (1) the FLC scattering process exert mostly on energetic ions above 30 keV on the nightside where the magnetospheric configuration is more stretching. Such ion loss thereafter leads to a faster recovery of the ring current. (2) The FLC-associated ion precipitation mainly occurs in the outer region (L>5 for protons and L>4.5 for oxygen ions) on the nightside, and the oxygen ion precipitation takes places in a wider region than protons although its intensity is much lower. Comparisons with POES observations suggest that more precipitation is needed in the inner region, implying that other loss process is required in the model. (3) We further found that the precipitating energy flux of protons due to the FLC scattering can sometimes become comparable to the one from the electrons on the nightside, although electrons usually dominate the ionospheric energy deposit from the midnight eastward towards the dayside. (4) Finally, the FLC scattering process seems to be capable of explaining the formation of the isotropic boundary in the ionosphere.