The insulating material flashover induced by an electrostatic electromagnetic pulse radiation field in a complex electromagnetic environment is a big concern in spacecraft surface materials. Polytetrafluoroethylene (PTFE) is the most often used insulation material in spacecraft. For this reason, the secondary electron emission avalanche (SEEA) model is proposed for the theoretical analyses of and experiments on the PTFE surface flashover induced by an electrostatic electromagnetic pulse radiation field. We use the current probe sensor to measure the induced flashover current waveform on the grounding wire and combine the probability of the electrostatic electromagnetic-pulse-induced flashover under different electrode voltages and electrostatic discharge (ESD) simulator output voltages. First, the SEEA theory is established considering the flashover voltage without an external electrostatic electromagnetic pulse field. The flashover voltage is then applied to the needle-plate electrode, and the distorted electric field is formed at three nodes of electrode–PTFE–air. Second, the flashover voltage with an external electrostatic electromagnetic pulse field is taken into account. The external field producing horizontal and vertical electric field components between the electrodes is fully investigated. Third, experimental results on the electrostatic electromagnetic-pulse-induced PTFE surface flashover using a needle-plate electrode structure are analyzed and discussed in detail. All findings are supported by the proposed SEEA model in an electrostatic protection using PTFE material.