A new finite element simulation model based on two trochoidal tool-paths was constructed, and was used to simulate a full immersed milling with three flutes cutter. In this FEM model, the special method used here is to construct two trochoidal curves at the beginning with an offset value which is just equal to the feed value per tooth. These two linked trochoidal curves represent tool paths generated by two flutes respectively so as to construct the workpiece model. Cutting forces in the feed direction and in the normal direction were analyzed in detail. A verifying experiment shows this simulation is credible in general. This method can also be applied into situations of milling with more flutes such as face milling.