The optical-phonon deformation potentials (ODP's) of the tranary compounds Ga1-xAlxAs have been calculated by LMTO-ASA band structure technique combining with a virtual crystal approximation and a frozen-phonon model. The ODP's as a function of the Al composition x has been predicted. We find that the ODP's d0,d30,d10(val)and d10(cond) can be expressed as a quadratic equation of the compositions. Among them a small bending parameter is only connected with the d0 vs x, showing it to be a nearly linear dependence. The computational results also show that the d10(val) will equal to the d10(cond) at x≈0.65. So the ratio d30/d10 should be divergent at that composition. This fact implies that the contribution of the two-band term to the Raman tensor of the first-order resonance Raman scattering for energy gap E1-E1+△1 can be neglected at that composition in Ga1-xAlxAs. The reliability of our calculation results has been verified by using the relationship between the ODP's.