Full-Potential-Linear-Muffin-Tin-Orbital(FP-LMTO) method was employed to study t he structure and magnetism of iron.The three possible structures of iron were in vestigated over a range of atomic volumes in three magnetic states respectively. The total energies and magnetic moments in various volumes were obtained.The rel ations of pressure vs volume and bulk modulus vs volume were deduced also.The st ructural and magnetic stability of all the possible phases was discussed in diff erent ranges of atomic volume.The α→ε phase transition pressure was evaluated .By comparing our results with the experimental ones,they are in good agreement.