This article discusses the optical transmission performances of phase-change optical devices. A bending waveguide model covering Ge2Sb2Te2 (GST) thin films was established using the finite difference time domain method. The influences of the GST area,thickness, and position in the bending waveguide on the optical transmission efficiency and loss were obtained in both the crystalline and amorphous states. The results indicated that when the optimal coverage area of the GST was 0.415μm2, and the thickness was 17nm, the optical transmission of the device was not affected by the GST position. The maximum contrast of the optical transmission reached 90.8%, and the insertion loss was as low as 0.321dB. Broadband parallel transmission could be achieved in a wavelength range of 1500~1670nm. The device had a small size and high extinction ratio, which theoretically met the requirement for enhancing the accuracy of optical calculations. This study is significant in the development of non-volatile,parallel integrated photon matrix computing unit devices.