Using a tight-binding bond orbital model, the local atomic structure of solid solution is calculated. The results are compared with theoretical results obtained by the valence force-field model calculation and experimental results obtained by extended x-ray absorption fine structure measurements and are found to be in good agreement with experiments. The calculated bond polarities, the bulk modulus, elastic constants, force constants, Young's modulus and sound velocities of GaAs and GaP are in good agreement with the existing experimental data. All of the results of alloys are predicated in the virtual crystal approximation. It is found that the bulk modulus, elastic constants, force constants, Young's modulus and sound velocities monotonically increase with increasing P composition and the increase is dominated by the change in average bond length. The electronic band structure of is obtained. The crossover composition . The results of the direct-band-gap energy are in very good agreement with the photoluminescence measurement data. The effective electron mass associated with the conduction band minimum in direct-band-gap alloy is estimated based on the theory and is in good agreement with the optically detected cyclotron resonance and magnetoluminescence experimental results.