At present, both the power-frequency test method and the low-frequency sine-wave test method for the excitation characteristic test of the current transformer for protection have some shortcomings. Aiming at these existing problems, this paper establishes an analysis and calculation method of excitation characteristic test for protection current transformer with ultra-low frequency arbitrary waveform signal source according to the Lucas model. In this method, the excitation current of current transformer is separated into eddy loss current and hysteresis loss current, and the related parameters are measured, such as transformer core loss, basic magnetization curve and limit hysteresis loop. The influence of voltage drop on DC resistance is fully considered, and the excitation characteristic data under power frequency are obtained by calculation. In this paper, a breakthrough have been made in the restriction of excitation characteristic test by the traditional way of using power frequency and low frequency sine wave, we fully consider the influence of the core saturation, hysteresis and direct resistance of current transformer, and establish a model and a calculation method for arbitrary waveform. Various experiments and comparisons proves that the method proposed in this paper is accurate and reliable.