The method is developed in this paper for optimum designing the holographio concave grating (HCG) that can be used in the scanning flat spectrometer from the general aberration theory of HOGs and the character of the mount of the grating. The design program is simplified through transforming the complicated integration in to the sampling summation over bhe scanning range of angle and the spectrum planes. As a practical example, an astigmation corrected scanning flat holographio concave grating (SFHCG) is designed and some results of the numerical and optical experiments are given.