In this work, a novel positive pulsed wire-plate-wire (w-p-w) streamer discharge reactor is developed by introducing a floating plate electrode based on the previous wire-wire (w-w) reactor to attain a larger plasma propagation and improve the toluene degradation performance. The streamer propagation characteristics, distribution of ·OH, toluene degradation efficiency, and process efficiency of reactive species production of the w-p-w reactor were studied and found to be highly related to the position of the floating plate electrode. ICCD images show that an intensive negative streamer can be generated from the ground electrode in the w-p-w reactor, which differs from the corona-like negative discharge in the w-w reactor. The position of the floating electrode decides the distance of the positive discharge (d+) and the negative discharge (d-), subsequently affecting the reactive species production and toluene degradation of the w-p-w reactor. When the d+/d- reaches 1:1 where a relatively symmetrical and even distribution of ·OH is achieved over the discharge gap, the toluene degradation efficiency and CO₂ selectivity is 17% and 14% respectively higher than that of the w-w reactor at 230 J/L. According to a kinetic model including competition by the reaction intermediates, the highest process efficiency of reactive species production is obtained when d+/d-=1:1 in the w-p-w reactor, consistent with its superior toluene degradation performance. FTIR results indicate that the types of toluene degradation byproducts are not affected by the insertion of the floating electrode, however, a more thorough toluene degradation can be achieved in the w-p-w reactor.