Support Vector Machine(SVM) has been widely applied to classification and regression problems．Because there is no probability output but lattice output only in SVM，this paper puts forward a kind of credibility prediction function with weighted average．Through this function，the degree of belief corresponding to every predicted value can be calculated，adopting a tolerance of credible level on the predicted value．Simulation results with the general Linear Frequency Modulation(LFM) Chirp signal on radar indicate that，this method not only realizes calculating the degree of belief for prediction，but also can offer qualitative analysis for the noise content in signal．