The tire for automobile is consisted of several layers and the final layer is called by tread. The tread is manufactured by co-extrusion of rubber compounds. The die for tread extrusion consists of three dies, insert die, performer die, and final die. Computer simulation has been performed to design the insert die and performer die. Non-isothermal non-Newtonian material model for rubber compound was used in the simulation. Flow patterns such as velocity distribution and velocity vector, temperature distribution, pressure distribution, and wall shear stress distribution have been compared according to the die design. The results of computer simulations can be used for not only design of co-extrusion die but also trouble shooting of tire tread extrusion problems.