In order to reduce the length of polymer branch waveguide in Mach-Zehnder(M-Z) electro-optic polymer modulator, asymmetric sine-bend ridge waveguide is researched. The transmission loss of asymmetric sine-bend ridge waveguide under different parameters is systematically studied by using the full-vector finite-difference beam propagation method (FD-BPM). The structure is optimized as ridge width w=4 μm, branch height h=11 μm, slab width on core layer of outboard bend s=2 μm, and length of the bend waveguide L=300 μm. The research results have shown that if the symmetric sine-bend ridge waveguide is replaced by asymmetric sine-bend ridge waveguide, the length of branch waveguide can reduce 40% under the same transmission-loss conditions. The results will have a certain reference value to the design of optical waveguide in polymer M-Z modulator.