Abstract: A mechanical stability criteria is used to investigate the mechanical propoties of metal Al.The method is applied to calculate the tension strength of Al crystal by the EAM potential proposed by A Voter et al when the crystal is subjected to an uniaxial tension or compression along100 direction.Under compression the crystal structure is transformed from FCC into BCC and then from BCC into BCT.The BCC and BCT structures are unstable.Under tension the crystal is destroyed,when the thoeretical strain arrives at 14.42% and the corresponding theoretical strength is 0.64×10⁴ MPa.From above calculations it is obtained that when the strain of the deformed crystal is out of the range from-11.56% to 14.42%,the EAM potential is not suitible to describe the mechanical properties of metal Al.