In this paper, a single-filament schlieren system equipped with a four-element photodiode was developed to investigate the disturbance in the discharge region of a pulsed gas laser. This method showed a high sensitivity in measuring weak disturbance left in the test region. Therefore, it was applied in a discharge-pumped ArF excimer laser for the acquiring of optical disturbance of the gas medium in the directions of pulsed discharge and gas flow simultaneously. Time-resolved signals of the optical disturbance were recorded for each pulse. A quantitative evaluation for the strength of residual disturbance was obtained from the differential output of the four-element photodiode, and the influence of the disturbance on the pulsed energy was also analyzed. It showed that this method can be easily applied in pulsed gas laser to study the effect of the gas non-uniformity on beam parameters.