There are two major errors in predict ing Space Object (SO) ephemeris (state vector): one is the error of the Initial Orbital Element (IOE) sets, the other is that of the Dynamical Model (DM). In order to get a better predicted ephemeris, a better IOE or/and DM is needed. This paper aims to seek a method of improving the precision of IOE and PM together. The basic idea is to reduce the error of semi-major axis (a) together with that of the Area-Mass ratio (A/M) by calibrat ion. The fundamental principle is that the error of a and A/M would propagate and augmented with time symmetrical in down-track component, the necessary condition is that the precise ephemeris of the past must be obtained.