The invention relates to a merging-sorting method based on an assembly line process and a valve control device using the merging-sorting method. The merging-sorting method is an effective parallel algorithm based on merging operation. Merging-sorting is operation for combining two ordered arrays into one ordered array; elements in the two arrays are compared, and smaller elements are put into a third array, and so forth; and if one of the arrays arrives at the end firstly, the remaining parts of the other array are put into the third array, so that the two different arrays are combined into one ordered array. Moreover, the method is applied to a valve control system of a flexible direct-current power transmission system, and a key path in the algorithm is shortened by means of an assembly line technology, so that the speediness of capacitive voltage sequencing can be ensured under the situation that IGBT (Insulated Gate Bipolar Translator) sub-modules of each bridge arm are increased; less resources are occupied; and the utilization ratio of a chip is increased.