The dipole moment-based reciprocity to model intra-system electromagnetic interference (EMI) in wireless devices is proposed in this paper. In this model, the decomposition method based on reciprocity is used to calculate the coupling voltage on the victim antenna. The original noise source is replaced by equivalent dipole moments in the forward problem while electromagnetic fields on the locations of dipole moments are scanned in the reverse problem. The proposed model has been validated with full-wave simulations and measurements; it provides not only convenience to estimate radio-frequency interference (RFI), but also physical insight to understand the intra-system EMI problem.