It is foundry trade puzzle all along for precise determination of C element composition for nodular graphite iron liquid metal using atomic emission spectrometry， The scientific instrument for determination calibration is ok，be unequal to measures a product composition the certain reality and objective because there is magnitude at preparation of samples error，Clear method for preparation of samples not be given in GB/T20066-2006 for determination for nodular graphite iron liquid metal，there is not unification method for product process control at application corporation. The precise diagnosis product chemistry composition can lower suspect product amount and quality control cost. This paper introduction of authentication method and solving technique puzzle for precise determination of chemical composition for nodular graphite iron liquid metal using atomic emission spectrometry.