The analytical description of the melt flow within the co-rotating twin screw extruder has been issued in various publications and it is an integral part of calculation models, software solutions for simulating polymer compounding processes such as SIGMA. Nevertheless, the accuracy of an analytical model depends on the defined simplifications. The more simplifications within the analytical description, the more deviation between the technical system and the calculation model. Analytical models for twin screw processes are no exception and are subject to simplifications and adaptations due to the complex geometry and the transient flow field. Therefore, the use of the kinematical inversion principle, the exchange of the original screw channel geometry and the consideration of an evenly distributed pressure gradient are commonly used simplifications for calculations models. In this paper a new analytical approach to calculate the melt flow is presented. The model is based on numerical simulations and with the use of the performance mapping method an analytical calculation method is derived. The advantage of the performance mapping method is that the original geometry and kinematical behavior of the twin screws are considered and the transient flow field in the system is used to generate a wide range of performance maps. Within the scope of this work, the performance maps of the melt conveyance and the pressure gradient in the fully filled screw channel are quantitatively examined with the aid of specially defined evaluation routines. Characteristic operating points are identified by the conveying characteristics of the melt which are displayed in the performance maps. The validation of this new analytical approach by using the performance mapping method with numerical data demonstrated that the two-dimensional description of the melt flow within the screw channel flow has a deviation of less than 10 % for varying flow law exponents geometry and process parameters.