Variable optical attenuator (VOA) is one of the key devices in Dense Wavelength Division Multiplexing (DWDM) network. This paper proposes a method of designing a couplingbased VOA. The VOA uses three channel waveguides and utilizes the electrooptic effects of polymer. The Beam Propagation Method (BPM) analyzes and simulates the qualities of this device. The results show that the VOA achieves nearly 60 dB loss with a low insert loss (0.48 dB) and the drive voltage is 11.7 V. This design reduces the drive voltage effectively, and realizes a large loss.