Molecular dynamics method was used to simulate tensile deformation of the high-purity single-crystal tungsten nanowire prepared by the metal-catalyzed vapor-phase reaction method first proposed by our research group. Stress-strain curve and microscopic deformation structure were analyzed in order to reveal the tensile deformation characteristics and microscopic failure mechanism of the single-crystal tungsten nanowire. Results show that the whole stress-strain curve can be classified into five stages: elastic stage, damage stage, phase transition stage, hardening stage and failure stage, where the phase transition is the main reason for hardening of the single-crystal tungsten nanowire. The first stress drop is caused by irreversible change of the local atomic dislocation and twinning, and the second stress drop is due to lattice structure failure resulting from the local atomic dislocation of the strengthened material and the development of split-forming necking area leading to the fracture of single-crystal tungsten nanowires. Calculated result of the elastic modulus is in good agreement with the test results of elastic modulus of the single-crystal tungsten nanowire.