In order to reduce length of the branch waveguide in Mach-Zehnder (M-Z) electro-optic modulator, the organic polymer ridge waveguide with asymmetric structure is applied in S-bend waveguide. Using the semi-vector finite-difference beam propagation method (FD-BPM), the transition loss of TM00 optical field is systematically studied in three conventional bend waveguides, namely sine-bend, arc-bend and cosine-bend, under different parameters, which is compared with the S-bend waveguide using symmetric ridge waveguide structure. The research results show that the lengths of sine, arc and cosine branch waveguides could be reduced by 40%, 30% and 25% respectively in the same transmission loss conditions, when the structure parameters are core height h=1.5 μm, ridge width w=4 μm, branch height G=11 μm and ridge height is 0.3 μm, in the case of short core width s≥2 μm. The results will have some reference value to the design of optical waveguide in M-Z modulator.