The Johnson-Cook model and gradient-dependent plasticity were used to investigate the adiabatic shear band (ASB) width and the ambient temperature effect for Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, which was similar to the viewpoint proposed by Batra and Kim. Theoretical results show that at higher ambient temperatures, the ASB is wider, as is in agreement with many experimental observations. At higher total ASB widths, the ASB width-ambient temperature curve is slightly concave-upward. However, at lower total ASB widths, the ASB width-ambient temperature curve is approximately linear. These new phenomena cannot be predicted by the famous Dodd and Bai’s model. The calculated ASB widths are closer to the measured results by Liao and Duffy. A simple expression for the ASB width was derived under the condition of neglecting the strain-hardening effect and adopting the linear softening model and gradient-dependent plasticity. It is found that higher ambient temperature, density, heat capacity, softening modulus and shear stress, or lower work to heat conversion factor and shear strength lead to lower adiabatic shear sensitivity and wider adiabatic shear band