Calcium ions play crucial roles in many important biological processes, such as muscle contraction, signal transduction in nervous system, cell signaling regulation and cell fate determination. In the last few years, a couple of novel structures of Ca2+ permeable ion channels have been determined, which makes the computational studies of the Ca2+-related bio-molecules highly desirable. However, the existing Ca2+ models in the classical non-polarizable force field are inaccurate in calculating the interaction energies between calcium ions and protein molecules, which has hindered the relevant computational studies. We are developing a new Ca2+ model in the framework of the classical non-polarizable force field. The aim is to not only reproduce the energetical and dynamical properties of calcium ions in solution, but also better describe the interaction energies between calcium ions and proteins. Although still under development, the new Ca2+ model has shown very promising results in terms of permeability through ion channels in our simulations. It will probably allow many bio-molecules interacting with Ca2+ to be simulated in a more quantitative way.