In fiber melt spinning, a bunch of polymer melt filaments are continuously drawn and simultaneously cooled with air in order to obtain solidified yarns, which later compose the synthetic fiber in the bobbin. Melt spinning is a basic non-isothermal operation in the production of synthetic fibers, and the velocity and temperature fields in the filaments can be useful to control the quality of the final product. Therefore, the research of the temperature and the speed in the spinning path will be very important. Based on the theory of melt rheology, the co-extrusion morphology and performance of polymer melts PA6 /PET which extrude from circular spinning porous are simulated using finite element method. The effects of the fluid flux ration、cooling air temperature and winding speed on co-extrusion fiber interface and spinning process temperature are analyzed. And the simulated results show that the interfacial offset increases with the increase of the flow rate ratio of two polymers; changing the cooling air temperature, the temperature distribution has the same trend; low winding speed is conducive to the convergence of stretching rate. The simulated results can dynamically and quantitatively reflect the melt flow process, and these results can make guiding sense to engineering application.