In high power excimer laser system, due to high gain and nonstorage medium, amplified spontaneous emission (ASE) is the key factor impacting on the signal contrast of the system output. In angular multiplexing master oscillator power amplifier (MOPA) laser amplifier chain, combination of the electro-optical switch and gain control method is used to suppress ASE. An electro-optical (E-O) switch is plugged after the first amplifier, and the other polarizer component of the analyzer is used for controlling the light beam and as gain controlling beam of the next amplifier. The optical path is constructed, principle experiments are carried out, and signal contrast up to 403001 is obtained in the second pre-amplifier. The advantages of this method are less energy loss and lower damage threshold request. The combination of E-O switch and gain control method gives a good solution to the ASE suppression of the first two pre-amplifiers.