Abstract: With the rapid development of DC transmission technology, the operational reliability of cross-region HVDC systems plays an increasingly important role in the secure and stable operation of power grids, so it is significant to evaluate the HVDC scientifically and reasonably. The main reliability indexes of HVDC systems collected domestically and internationally, including the number of forced outages and energy availability, were compared, and analyzed in this paper. The main factors affecting the reliability indexes were pointed out, and a reasonable range of reliability indexes was proposed based on the characteristics of domestic HVDC systems. A comprehensive reliability evaluation index considering both the safety and the benefit of DC equipment was constructed, and suggestions on further improving the HVDC's reliability put forward.