Two positive cloud-to-ground lightning spectra have been captured by a slit-less spectrograph. In combination with the synchronous electric field change waveshape, the discharge characteristics along the channel have been investigated. The results show that the total intensity of ionic lines in spectra and the electrical conductivity increase with the increase of channel height. According to the positive correlation between the total intensity of ionic lines and the discharge current, it is found that the current intensity of downward positive cloud-to-ground lightning increases with the increase of channel height. Comparing it with the reported current attenuation along the channel of downward negative lightning, it is deduced that the increasing or decreasing of the current along discharge channel is likely to be related to the current direction.