According to the microwave properties of the traveling-wave electroabsorption modulator (TW-EAM) transmission line, an equivalent circuit model was presented and a GaAs/GaAlAs TW-EAM for 850 nm has been fabricated. The influence of the ridge width on the frequency bandwidth was driven by analyzing the characteristic impedance Z_0, microwave transmission constant γ and S_ 21. A reduced velocity mismatch between optical wave and microwave and an impedance mismatch were demonstrated for the narrower ridge width. Potential frequency bandwidth of 23.9 GHz of a TW-EAM was predicted by theoretical simulation when the ridge width was 2 μm.