The spin-dependent transport through double quantum-dot-array coupled to a single quantum dot is studied by using the non-equilibrium Green function formalism. Due to the quantum interference and the spin-dependent phase induced by Rashba spin-orbit interaction, the spin of the electron through the device is polarized. When the energy level of quantum dot is in the bias window, the spin accumulation in the single quantum dot can maintain a large value in a wide range of energy and the quantum dot is largely spin polarized. The spin accumulations in the single quantum dot under positive bias and negative bias are absolutely different because of asymmetric quantum dot structure. These results is helpful for designing and fabricateing the practical spintronics devices.