Abstract: With the increase of working frequency, electromagnetic interferences (EMI) become more and more serious for electronic equipment. High-speed connectors are the main interference sources. Numerical simulation of EMI/EMC for complicated communication system still suffers from many challenges such as too many complicated details, wideband frequency response, and inconsistency with real testing. In this paper, a simplified simulation model is proposed firstly with the aid of measurement and theory of reverberation. Then, a cooperative simulation is achieved through domain decomposition method (DDM). Furthermore, a superposition method is adopted to investigate the random effect brought by the uncertainty of transmission signals. The resonance and loss characteristics of chassis can be modeled exactly by the proposed method. Besides, the analysis of random effect is simplified. Consequently, the leakage field through the chassis is accurately predicted.