1. A echo cancellation system, comprising: a speaker, for outputting a acoustic signal, which is represented as x(n); a microphone, for receiving an input audio signal, which is represented as d(n); a convergence statistic generator, receiving the input audio signal, the acoustic signal and a error signal, for generating a convergence parameter; a variable step-size generator, receiving the error signal and the acoustic signal, for generating a step size parameter in accordance the error signal and the acoustic signal; a decision device, receiving the convergence parameter and the step size parameter to output a adjusted step size parameter, wherein the adjusted step size parameter is equal to a boundary value when the convergence parameter is greater than a convergence threshold, wherein the adjusted step size parameter is equal to the step size parameter when the convergence parameter is smaller than the convergence threshold; an adaptive weight control unit, receiving the acoustic signal, the adjusted step size parameter and the error signal to generate a coefficient vector; a transversal filter, receiving the acoustic signal and the coefficient vector to generate a echo cancellation signal; and an error signal generator, receiving the input audio signal and the echo cancellation signal to generate the error signal in accordance with the difference between the input audio signal and the echoless output signal.