The present invention discloses a parameter obtaining method and apparatus. In this method, multiple signals are received over a communications link on a network, where each of the received signals is corresponding to a point on a complex plane; decision is performed on each of the received signals; for each of the received signals, an error signal between the received signal and a corresponding decision signal is determined; and a complex-plane distribution feature parameter used to indicate a distribution feature, on the complex plane, of the signals received over the communications link is determined according to all the determined error signals. In this method, an inaccurate maintenance result in manual analysis of a constellation diagram is avoided.