In industrial melt spinning processes, there is a leading-order radial temperature variation. For viscoelastic flow, the radially nonuniform temperature causes, through thermal history, the radially nonuniform stress, which results in nonuniform crystallinity and fiber microstructure. Therefore, we use a 2-D approach to study the nonisothermal melt spinning with ongoing crystallization. In the mathematical. formulation, the phase transition (from amorphous phase to crystalline phase) is described by the equation proposed by Nakamura et al. [K. Nakamura, K. Katayama, T. Amano, J. Appl. Polym. Sci. 17 ( 1973) 1031-1041]. The crystallization rate, which is a function of both temperature and molecular orientation factor, is evaluated with the equation proposed by Ziabicki [A. Ziabicki, Fundamentals of Fiber Formation, Wiley, New York, 1976]. The constitutive equation used is the nonisothermal PTT model, which is converted from its isothermal form with time-temperature superposition. The above formulation was implemented in Polyflow. A nonisothermal melt spinning process of Nylon 6 was simulated. We verified numerical results by comparing, either quantitatively or qualitatively, the experimental observations. We demonstrated the structure of the 2-D solution and its influence on spun fiber property, birefringence, which are of practical importance and need to be taken into account in fiber product and process design.