An improved method, which is based on the harmonic-balance technique, for speeding up the convergence of iteration procedure is presented. As example, it is applied to the nonlinear analysis of microwave mixer, in which a simple time domain to frequency domain transformation technique for the mixer diode is introducel. The use of this technique saves computing time dramatically. And the analyzing results are in good agreement with the results published. The improved method can also be extended to the CAA of nonlinear circuits with multi-devices.