Noise source reconstruction (NSR) is a widely used technique in radiated EMI analysis. Based on the voltage driven model presented by Hubing T.H., radiation resistance is an important parameter for antenna model and EM field estimation. Due to low precision, a novel method is proposed to determine the radiation resistance accurately. Electric dipole model and rod-shaped antenna model are established to improve the precision due to different frequencies of noise sources. The theoretical analysis and experimental results show the suggest approach good validity and realization.