Optical emission spectrum of aluminum plasma induced by a 1064 nm Nd:YAG laser is investigated by an Optical Multichannel Analyzer (OMA). Spectroscopic study shows that more number of Al, Al+, and Al++ spectral lines can be observed with increasing the incident laser fluence. Al, Al+, Al++ spectral lines are also observed successively with high fluence. The atomic spontaneous radiation is analyzed to interpret the calibrated plasma spectrum. The laser energy threshold for the appearance of excited Al, Al+, and Al++ spectral lines are about 0.8, 1.0 and 1.5 J/cm2 respectively. Assuming LTE (Local Thermodynamic Equilibrium) conditions, the plasma density is derived to be in the range of 0.7×1017 to 2×1017 cm-3 from the profiles of Al+ (358.7 and 286.1 nm) spectral lines with different gated times and incident laser fluences. The plasma temperature is also estimated to be 4000 ~ 8000 K, from relative intensities of two different Al I spectral lines (309.2 and 396.2 nm) with different fluence.