The traditional FD method is based on state-space diagrams, which would be extremely complex if the number of system states increases. A modified FD method is proposed and applied to the reliability assessment of the VSC-HVDC transmission system. In the proposed method, parameter matrices, including capacity matrix, probability matrix and departure rate matrix, are introduced into the reliability evaluation procedure to replace the state-space diagrams. A case study is conducted on the basis of the proposed method. Results show that the matrix based method overweighs the traditional FD method on both the calculation speed and simplicity, thereby providing an efficient approach to assess the reliability of VSC-HVDC transmission system. Furthermore, the impact of parameter variance on the system reliability is analyzed in order to identify the weakest component in a VSC-HVDC transmission system.