Abstract: Solar Proton Events (SPE) bring a significant radiation hazard to spacecraft and astronaut within and beyond the magnetosphere. Knowing and understanding the rule and precursor characteristic, establishing accurate prediction model to carry on the forecast of solar proton events, taking protective measures are of vital significance for the safety of the spacecraft and astronaut. Massive research has indicated that, before the eruption of solar activity, part of energetic particles may escape the binding of active region magnetic field, and disseminate towards interplanetary space along magnetic field line. Therefore, before the proton events, an increase of high energy proton flux may be seen in the earth-synchronous orbit. The proton energy spectrum before solar proton events which related with the solar nearby acceleration process has obvious difference with that of the general proton flux stochastic fluctuation. Therefore we may carry on the forecast of solar proton events through analyzing the energy spectrum parameters of proton before event. According to the proton energy spectrum, the variation of energy spectrum parameters before the commence of SPE was analyzed in this paper with proton flux data from channel 4~9 MeV, 9~15 MeV, 15~40 MeV, 40~80 MeV on the GOES satellite. A new method was introduced to use the variation of energy spectrum parameters and the proton flux data with energy E>10 MeV to predict SPE. Then, the method was used for SPE forecast based on the five-years data selection in 2002---2006 by test. The result turned out to be encouraging with the accuracy rate reaches to 97.5 % and have an advance time of several tens minutes up to over a hundred hours.