The Hayabusa spacecraft embarked on its return trajectory to Earth, after its touchdown on the asteroid Itokawa. During the cruise phase Sun-pointing mode, the spin-axis of the Hayabusa performs a coning motion under the solar radiation pressure effects. The effect mainly originates from the diffuse reflection of the solar radiation pressure on the solar array panels. In the simple analysis of this coning motion, however, the diffuse reflection coefficient is inconsistent in comparison to the typical diffusive parameter of the solar array panel. This discrepancy must be clarified by constructing a more accurate model of the solar radiation pressure in order to be able to dissolve the uncertainty during the return phase of the Hayabusa spacecraft. The accurate model should also be able to support the extremely precise navigation during the return phase to the Earth. This paper presents the precise model of the solar radiation pressure of the Hayabusa spacecraft and the estimation method for obtaining the optical parameters of the solar radiation pressure model.