A standard evaluation method for the multimode polymer optical waveguides is necessary to obtain reliable experimental results. There are several categories of evaluation techniques proposed by the International Electro-technical Commission (IEC). We have developed a simple input launch configuration to control mode evolution in the multimode optical fiber by means of the Encircled Flux (EF) category. Furthermore, we have examined our input launch system by evaluating insertion loss of the multimode polymer optical waveguides. The experimental results demonstrated the insertion loss variation of less than 5 %.