The present invention relates to a control method and a control system of a converter valve trigger angle of a direct current transmission system. Controlling a trigger angle of a converter valve on an inverter side comprises: when a direct current increases or a commutation voltage decreases, and an extinction angle decreases to a set predictive control setting value, applying an extinction angle predictive control policy to the converter valve; and according to the direct current and the commutation voltage, solving the trigger angle of the converter valve of the time when the extinction angle is equal to the predictive control setting value, in order to control the trigger angle of the converter valve. The control manner has an advantage that the predictive control can determine the trigger angle according to a real-time change of a system operation status, and an advantage of the control policy is used to overcome a defect of a traditional control method. Moreover, the control method fully meets requirements of relevant standards, parameters of the control method can be conveniently adjusted, and the control method is good in control performance, thereby increasing the system operation stability and suppressing occurring of commutation failures.