Abstract: Using the technique of short pulse generation by electro-optical (E-O) switches, a method for amplified spontaneous emission (ASE) suppression of the excimer lasers amplifier chain is established. An ultraviolet E-O switch with high contrast ratio was produced, and its principle experiments were carried out. The switch was applied to ASE suppression of the first pre-amplifier in excimer single-channel master oscillator power-amplifier (MOPA) system. The experimental result shows that the contrast ratio of the E-O switch is more than 2000, and the signal contrast ratio of output pulse of the pre-amplifier is promoted to over 20 000 after clipping. The result is beneficial to the following amplification of the laser pulse signal in the system, and provides a technical support for the system to obtain narrow-pulse signal output.