With the advancement of dual carbon strategy, distributed photovoltaic (PV) penetration continues rising in distribution network. It causes electromagnetic compatibility (EMC) which challenges the stability of power grid. This paper studies the key electromagnetic phenomena and their influence, systematically. The results show that high-frequency switching inverter generates harmonic pollution, particularly parallel multi-inverter resonance, switching transients induce electromagnetic interference (EMI), and the faults of control system could lead to DC current injection. These issues are more serious in the weak nodes with high penetration of PV, prominently. The paper proposes a multi-level mitigation framework, device-level solutions, and system-level measures. The research could provide the theoretical and technical guidance for the high-penetration of PV in distribution network.