Based on the LDO regulator DC offset failure mechanism under electromagnetic interference (EMI) study, the immunity modeling and simulation methods are proposed. A test chip was designed with novel on-chip voltage sensor which is implemented to test the EMI propagation inner LDO regulator. In the immunity modeling process, an equivalent circuit model dedicated to susceptibility prediction was built and validated by DC functional and Z parameter impedance measurements. In the simulation flow, the key sub-circuits and parasitic elements were analyzed to reveal the weight contributions on immunity issues in frequency domain. The DPI measurement results show a good fit with prediction from the model up to 1 GHz.