Solar Proton Event (SPE) has great influence on the human space activities. Establishing prediction model for total fluence of solar protons accumulated during a mission and taking protective measures are of vital significance for the security of the spacecraft and astronauts. Based on a data set of proton events from the last four solar cycles, a new statistical model is designed to predict the proton fluence for space mission analysis. The energy ranges considered are E>10 MeV and E>30 MeV, respectively. Because of the quasi-random nature of the occurrences, and spectra of SPE, solar proton mission fluence must be treated statistically. The purpose of this analysis is to derive the probability of exceeding various proton fluence as a function of proton energy and mission duration. Compared with commonly used JPL model, solar activity levels are taken into account to obtain the occurrence probability of proton events. The new model can access proton fluence in different phase, and is more consistent with the distribution of proton events.