This paper examines the electromagnetic interference (EMI) characteristics of driver units in flexible DC transmission systems, focusing on two specifications: 500 kV/3 kA and 800 kV/5 kA. Using simulation models and data analysis, the study compares the magnetic field strength distribution, intensity variations, and the contribution of different sub-modules. Results show that the 800 kV system exhibits a 74% to 76% increase in magnetic field strength, particularly in the Hy component, due to higher current and more compact design. Magnetic field strength increases across layers, with the fourth layer showing the most significant change. The compact design intensifies the magnetic coupling effect, leading to stronger interference in both core and edge modules. These findings highlight the need for improved electromagnetic compatibility (EMC) and anti-interference measures in high-voltage transmission system design, providing valuable insights for enhancing the reliability and stability of flexible DC transmission systems.