Empirical tight binding potential has been used in molecular dynamics studies of the local atomic structural order and defects in liquid and glassy Al under high and normal pressures. Results are reported for some solidlike clusters and structural properties of liquid aluminum. The simulated pair correlation function of the liquid Al is in good agreement with the experimental results. Both a structure very close to an ideal icosahedron and a structure related to a defective icosahedron are found. The fivefold symmetric structure plays an important role in glass formation. The fcc structural unit is demonstrated in glass by the existence of 1421 bond pair, but only in small proportion. The effect of high pressure on the supercooled liquid and glass is also studied. High pressure causes the nearest neighbor distance to shorten. High pressure favors the icosahedral and defective icosahedral structures. Glassy Al is an entanglement of a very large number of icosahedra and defective icosahedra which interpenetrate and share faces with each other. (C) 2003 American Institute of Physics.