Based on the theory of the ring current formed primarily through injection driven by strong convective electric fields, E×B drift and subsequent trapping of particles from the plasma sheet into the inner magnetosphere, and considering the ring current ion loss by charge exchange and ion precipitation, a model of ring current ion distribution during main phase of storm is improved and tested in this paper. We simulated the properties of ring current ions in magnetosphere during different levels of storm main phase, and investigated the response of the partial ring current to convective electric field. The simulation was satisfactory. The results showed that partial ring currents dominate the ring current during main phase with a set of asymmetries between dawn to dusk and dayside to nightside, ions precipitation and the anisotropic distribution of pitch angles. The convective electric fields are positively correlated to the ion flux intensity and the ion distribution ranges. The simulations accord well with the observations and are reasonable.