The characteristic parameters reflecting the current intensity in lightning return stroke discharge channel are the primary concern in the field of lightning physics research and protection. Based on the spectrum and the corresponding fast electric field change waveforms for 9 natural cloud-to-ground lightnings including multiple return strokes, part of the total charge quantity in the corresponding leader channel was estimated by different methods, and its influence on current intensity and spectral characteristics of return strokes were further investigated. The results show, that for the same lightning, part of the leader charge quantity estimated by using the two methods according to the electric field change waveforms is in good agreement with the electron number per channel length calculated by basing on leader spectrum, it is also found that part of the neutralized leader charges is positively correlated with the peak current, the radius of the core current-carrying channel and the total intensity of ionic lines in the spectrum. These results mean that the current intensity of the lightning return stroke discharge mainly depends on the charge quantity being stored in the previous leader process. The radius of the core current-carrying channel is closely related to the current intensity. Moreover, the intensity of the ionic line in the spectrum can directly reflect the current intensity, which is an ideal observable parameter for studying the current characteristics.