We present a novel GeSi electro-absorption (EA) modulator design on a silicon-on-insulator platform. The GeSi EA modulator is constructed based on the Franz-Keldysh (FK) effect. The light is evanescent-coupled into the GeSi absorption layer from the rib Si waveguide. A contnet of 1.19% Si in SiGe absorption layer is chosen for C (1528–1560 nm) band operation. Simulation shows a high (3 dB) bandwidth of ～ 64 GHz and extinction ratio of 8.8 dB. Especially the insertion loss is as low as 2.7 dB.