For the first time, highly efficient and flexible polymer light emitting diodes (PLEDs) based on silver nanowire (AgNW) electrode, with improved operational stability by simply applying pre-bias conditioning treatment, are demonstrated. Reverse bias conditioning performed before J-V-L measurement of the PLEDs enables the rough AgNW networks to function properly as a bottom electrode by stabilizing current characteristics, and the devices continue to show consistent operational performances. Conditions of applied bias and thicknesses of active layer are controlled for optimization and it is found that high reverse voltage is required to obtain current stabilization. Adequate thickness of polymer is also necessary to avoid breakdown induced by reverse bias. The essential effect of pre-bias conditioning on the improved performances of PLEDs is investigated, and it is found that morphological change of AgNW networks contribute to the improvement in device performance. Some of the AgNWs that appear to be pathway of leakage current are deformed, and surface roughness (RMS) of the AgNW film is decreased while the sheet resistance of the film is maintained when the reverse bias conditioning is applied. It is also revealed that pre-bias conditioning is independent from directionality of the applied bias when utilizing insulating polymer sandwiched between two electrodes.