For model reduction of flexible spacecraft, conventional first-order balanced truncation(FOBT) method will destroy the second-order structure and dynamic properties of original system. In order to overcome this drawback, a new structure-preserving approximated balanced truncation method for model reduction of flexible spacecraft was proposed. The modal cost was described by a cross Gramian and the closed-form solution of cross Gamian was obtained via special form of dynamical equation of flexible spacecraft. The new method preserves the second-order structure, symmetry and positive definiteness of the original system. The numerical results show that the new method is superior to conventional first-order balanced truncation(FOBT) method for improving efficiency without sacrificing accuracy.