A model has been developed to analyze the vapor phase epitaxial growth of GaAs1-xPx under different experimental conditions. The deposition process has been explained by a scheme of reactions. The equilibrium constant for each reaction has been deduced from thermodynamic data. The chemical species considered for the present investigations are AsH, PH, As-2, P-2, As, P, As3P, As2P2, AsP3, AsP, GaCl, AsGaCl, PGaCl, GaAs, and GaP. The growth rates of GaP and GaAs are derived in terms of partial pressures and deposition temperature by assuming the removal of chlorine from the complex molecules (AsGaCl, PGaCl) as the rate-determining step. The phosphorous composition x has been derived from these growth rate expressions. The surface coverage of the adsorbed species as a function of substrate temperature has been investigated. The numerical analysis of our results shows that the composition depends more strongly on partial pressures than on deposition temperature, and As is preferentially deposited compared to P. The validity of our model was tested by comparing our predictions with reported experimental data, and there is good agreement between them.