We present a methodology to construct a Ta-W cross potential for Ta-W binary alloys, in the second nearest-neighbor modified embedded atom method formalism, based on ab initio calculations. The first attempt has consisted in fitting the potential on a single reference structure, and has led to a poorly transferable potential, particularly in the W-poor region. Improving our procedure of parametrization by taking into account various structures to fix the angular screening parameters, we have been able to obtain a more transferable potential. The formation energies of some structures not used in the adjustment of the potential and energies of body-centered cubic solid solutions reproduce experimental tendencies. We have also tested the ability of our improved potential to predict melting temperatures of Ta-W alloys.