An ultra-compact rectangular Mach-Zehnder (MZ) interference Electro-Optic (EO) modulator on InGaAsP/InP platform was proposed. This modulator consists of novel trench couplers and 90° waveguide bends. T type microstrip Travelling-Wave (TW) electrodes were designed for the L-shape waveguide phase shift arm of the MZ modulator. First of all, an upper bandwidth limit of this modulator was evaluated by using an equivalent circuit model of the TW electrodes. According to microwave characteristics such as impedance match, return loss and bandwidth, the transmission and input/output of electrodes and structure parameters of transition regions were optimized through a finite element analysis method. The simulation results show that being limited by the input of electrodes and transition regions, the overall TW electrodes exhibit an impedance match of >42Ω, return loss of <－15 dB and bandwidth of 65 GHz. Experimentally the return loss of －12 dB and the bandwidth of >20 GHz are obtained in terms of the fabricated Ti/Au electrodes on an InP substrate.