A systematical analysis and design have been made for 1.30 μm/1.55 μm Si 1-x Ge x/ Si filters based on multi mode interference. Using the mode propagation analysis, transmission characteristics of the device were investigated. The results show that: 1) for 1.30 μm filter, the optimum coupler length is 2302.5 μm, and the contrast and insertion loss are 31 dB and 0.01 dB, respectively; 2) for 1.55 μm filter, the optimum coupler length is 2512.5 μm, and the contrast and insertion loss are 16 dB and 0.09 dB, respectively. For both of the filters, the Ge content x, rib height, and interfernce width are 0.04, 6.35 μm, and 8 μm, respectively.