 The crystal structures, elastic and anisotropic properties of CH3NH3BX3, B equals Sn, Pb, X equals Br, I, compounds as solar cell absorber layers were investigated using first principles calculations. The type and strength of chemical bonds between B and X atoms determine the elastic properties of these compounds. Organic cations and inorganic ions are important factors in determining the functionality of these absorbers. Bulk, shear and Young's Moduli range from 12 to 30 gPa, 3 to 12 gPa, and 15 to 37 gPa, respectively. The interaction among organic and inorganic ions has little effect on the elastic properties of these compounds. The B slash G ratio and Poisson's ratio indicate that the perovskite layer can be used as a flexible or stretchable layer on a polymer substrate. This is due to its low shear modulus and strong anisotropy derived from the elastic constants, chemical bonds, and symmetry. This article was authored by Jing Feng.