High voltage direct current transmission（HVDC） system is playing an increasingly important role in China and the relative researches， such as definition of reliability indices， reliability assessment， reliability evaluation， and reliability management for the HVDC systems， receive increasing attention. However， the present reliability indices and evaluation methods exist some problems. On the basis of the indices of energy utilization rate and the energy availability rate， the operation utilization rate is proposed and derived. It can be used to evaluate the loading intensity and utilization degree. The historical data of the practical HVDC systems are analyzed by the proposed index. The results show that the operations utilization index has a relative rational and clear representation of the status of the HVDC system and it can make appropriate tradeoffs between the dispatching sector and the operating sectors， which can in turn help to improve the reliability level of the power systems.