A systematic first-principles calculation of the linear and second-order optical susceptibilities as functions of frequency for CsGeBr3 is presented. Specifically, we study the relation between the structural properties and the optical responses. Three structural deformation factors, Δα, dGe, dX are used to express the degree of distortion from the ideal perovskite structure in bond angle, Ge position, and anion position, respectively. Based on our first-Principles studies, we find that Δα and dGe increase, while dX decreases as we substitute the halogen ion from Cl to Br and then to I. The dielectric function and the second harmonic generation coefficient are also found to increase with increasing Δα and dGe. Our calculation indicates that the direct bandgap, Eg, of CsGeX3 occurs at the R-point for all three compounds, and its magnitude decreases as Δα and dGe increase (i.e. Eg(CsGeI 3] < Eg(CsGeBr3) < E g(CsGeCl3)). Our partial density of states (PDOS) analysis reveals that the valence band maximun (VBM) and conduction band minimum (CBM) are mainly associated with the p-orbitals of Germanium. Interband and intraband analysed results for Χijk(2) CsGeBr3 can be separated into two main groups of peaks. One was contributed from the magnitude electronic bandgap; the other part was recognized to be attribution from the distortional structural factors. The magnitudes of Χijk (2) were in the same manner with some reported experiment near the band gap.