Pulsed discharge plasma over the liquid surface was observed in the needle electrode configuration. The characteristics of streamer propagation including its optical emission intensity were investigated by using the intensified charge coupled device (ICCD) camera. The experiment was conducted at 313 K, 0.1 MPa argon in a batch-type reactor with methyl orange as a starting material. The characteristic of pulsed streamers were started from the electrode placed above the methyl orange liquid surface and then reached the methyl orange liquid surface, where they propagated on it. The propagation of pulsed streamers and their progression distance increased with the increase in peak voltage value. The optical emission intensity increased immediately after the breakdown; and it increased to its peak value when the applied voltage reached its peak value. After pulsed discharge plasma treatment, methyl orange degraded into its derived compounds with the appearance of light color. UV-vis spectrophotometer analyzed that the intermediate compounds from the degradation of methyl orange consist primarily of aromatic compounds which contain nitrogen functional groups. The degradation of methyl orange is 99% when the number of discharge plasma was 20000x. With increasing the pulse discharge numbers, the pH and the conductivity of methyl orange solution changed clearly.