The invention provides a high-voltage direct-current power transmission system reliability assessment method considering an alternating-current side fault. A line commutated converter reliability modeling and probability index evaluation method is provided and is combined with an existing high-voltage direct-current power transmission system reliability assessment method, so that a problem that the influence on the high-voltage direct-current power transmission system reliability by the alternating-current side fault can not be taken into consideration by the traditional high-voltage direct-current power transmission system reliability assessment method can be solved. Therefore, precision and engineering practicability of the high-voltage direct-current power transmission system reliability assessment method can be improved.