Abstract: The second discharge characteristics of aluminum wire electrical explosion under various argon pressures were studied in a RLC discharge circuit. The results show that the curve of second discharge voltages by exploding aluminum wire presents a U-shape as the pressure changes. The spectrometer and high speed framing camera were used to study the radiation spectrum and spatial distribution of the electrical explosion plasma to clarify the roles of aluminum vapor and argon in the process of second discharge. It is found that argon participates in discharge process with the discharge channel along the surface of aluminum vapor at lower pressure, while the second discharge happens in aluminum vapor with the discharge channel inside aluminum vapor under higher pressure.