The Chinese Fusion Engineering Test Reactor (CFETR) is the next step in China's research into fusion energy. In phase I, the preliminarily design of diagnostic systems for the CFETR was completed; however, the material and spatial position of the diagnostic systems severely affect EM loads distribution in blanket modules. In order to evaluate the effect of a diagnostic port plug on the EM loads distribution in the blanket system of CFETR, a finite element (FE) model with an equatorial diagnostic port plug (EDPP) was established using ANSYS. The EM forces and moments are calculated and discussed, followed by a comparison of EM loads in the helium-cooled ceramic breeder (HCCB) blanket to verify the EM effect of the EDPP. Simulation results show that the EM loads in the inboard (IB) and outboard (OB) blanket modules and segments were changed with the EDPP, but the direction of the main loads on the blanket system did not change. The results also show that the EDPP has a greater influence on the EM loads of the IB blanket compared to the OB blanket, meaning it is necessary to take into account the effect of the EDPP during the evaluation of the mechanical design of the blanket system in further studies. The investigation presented here may also serve as a technical reference for the design and optimization of diagnostic port plugs in the future.