Based on ab initio methods and nonequilibrium Green's function theory, we have investigated the electronic transport properties of single and double 1，4-dithiolbenzene molecular devices which have different molecular relative orientations on molecule-metal contacts. Numerical results show that different molecular relative orientations have various influences on the electronic structure of molecules and current-voltage characteristics, which obviously affects the electronic transport properties of metal-molecule-metal systems. The equilibrium state of the extend molecule is not the best situation for electronic transportation. The characteristics of electronic transportation can thus be improved by adjusting the molecular relative orientation on molecule-metal contacts.