The high precision electrostatic accelerometer is one of the key payloads for Earth's gravitational satellite, and its sensitivity parameters directly determine the non-conservative force measurement, and eventually affect the precision of the Earth's gravitational field recovery. In this paper, the in-orbit gravitational calibration of the high precision space electrostatic accelerometer is discussed. A theoretical analysis shows that the two high sensitive axes of the SuperSTAR accelerometer with a resolution of 10^-10 m/s² used in GRACE mission can be calibrated by rotating a spherical attracting mass with a turn table.