In this paper, a technology on generation of ultrashort pulse with high extinction ratio is studied. The pulse from gain-switched DFB laser is linearly compressed in dispersion compensation fiber (DCF), then modulated synchronously by an electro-absorption modulator (EAM) by using the nonlinear absorption characteristic of EAM. With this method, ultrashort of 10.4 ps pulse with repetition rate of 10 GHz, low timing jitter, high extinction ratio and no pedestal is generated experimentally. The technology can be used in 40 Gbit/s optical time division multiplexing (OTDM) system. Also the result shows the ability of pulse shaping of EAM.