The diffusion process of intercalary species within insertion-host materials is the key step during the whole electrode reaction. Here a novel method based on the ratio (q) of the potentio-charge capacity to the galvano-charge capacity (RPG) was developed to determine the diffusion coefficient of intercalary species for porous electrode by the spherical diffusion model. By the RPG method, the Li+ diffusion coefficients within graphite were determined from the galvano–potentio-charge curves. The values of diffusion coefficient measured at different galvano-charge current or at different cutoff voltage suggested that the RPG method has a good reliability for determination of the diffusion coefficient.