In order to suppress the core-corona structures commonly observed in the single-wire exploding stage of wire array Z-pinch, the laser probe diagnostic is analyzed, and the exploding characteristics of aluminum wire under negative-polarity and fast-rising current pulses (90-170 A/ns) are investigated using a picosecond laser probe. The aluminum wire with a diameter of 15 μ m and a length of 2 cm, has a peak resistive voltage of 35-50 kV and a resistivity of 30-40 μΩ·cm before the voltage collapsed. The ohmic energy deposited in the load is 1.5-2.5 eV/atom at the voltage peak time, and 2.5-4.0 eV/atom at the time when the Joule heating power drops off to half of its maximum value. A faster rising current would lead to an increase of the energy deposition rate, and enhance the breakdown voltage. In most shots, nearly all the aluminum atoms near the electrodes are in the gaseous state, and liquid drops or clusters existing at the central part of the wire. While in some shots, the load is exploded into a gaseous state homogeneously along the axis. At about 127 ns after the laser peak, 70% of the initial mass is located within a diameter of 1 mm, and all the mass is within a diameter of 2 mm.