A method to assess signal transmission quality and the adjust method thereof are proposed. First, different time points of a control signal at a receiving end are acquired and the number of signal transitions in a predetermined time interval is counted. Next, the number of signal transitions is recorded and compared to a reference value to obtain a comparison result. The quality of the control signal is then determined based on the comparison result. The parameter setting of the receiving end is adjusted according to the quality of the control signal received by the receiving end to get a better performance setting.