A discharge pumped ArF laser oscillator amplifier system was improved independently,and a spectral width less than 0.020 nm had been obtained by using swept grating.The output of oscillator was injected into the amplifier,and the laser system produced 40 mJ/pulse,tunable,narrow spectral width and very low beam divergence laser.And the exact values of the wavelength as well as the spectral width of the ArF laser were measured b using Oxygen absorption spectrum.