1. An adjustable hierarchical scoring method, used in an adjustable hierarchical scoring system comprising a processor to perform the following steps of: generating a hierarchical scoring structure for speech-sound data; retrieving historical data of speech-sound scoring for the speech-sound data from a speech-sound practice database while a scoring result by a professional language instructor for the hierarchical scoring structure of the speech-sound data is being collected; performing a weight-adjusting operation according to the historical data of speech-sound scoring and the scoring result to calculate optimum adjusting weights for each layer of the hierarchical scoring structure; scoring retrieved speech-sound data of a student using a speech-sound scoring system; and performing a weighted average operation to the score of the speech-sound data of the student according to a corresponding adjusted weight, thereby generating the adjusted score of the speech-sound data of the student.