In order to study the adaptability of existing measuring instruments to the energy metering of Flexible HVDC system, a real-time digital simulation system based on modular multi-level converter (MMC) is developed based on RTDS system. The harmonic analysis and energy consumption analysis of the HVDC transmission system are carried out. Different types of meters are connected to the RTDS simulation system according to the specified wiring mode to study the adaptability of meters in the measurement of flexible HVDC transmission system. The main sources of energy consumption in flexible HVDC systems are connection transformer transformers and converters, and existing metering devices are suitable for this system.