Abstract: By using an isotropic diffusion statistic model with explosive discrete sources in an infinite galaxy, the transport equation for galactic cosmic ray proton is investigated. The non-steady state solution of the equation is obtained utilizing the very recent data of cross-section of P-Pinteraction and a reasonable diffusion coefficient. Then some features of the solution and the possible contribution to the proton spectrum from lots of this kind of sources are discussed. The expected spectrum can account for the experimental data quite well.