The combination forecasting model was building to overcome the potential errors generated by single forecast model on the basis of the grey system GM(1,N),multiple linear regression and back-propagation neural network,and the weighting coefficients were determined by the entropy method.The contrast test was conducted to predict the bearing capacity of PHC pile,and the results show that the method means absolute percentage error(MAPE) of GM(1,N) is 5.4%,the MAPE of multiple linear regression is 3.0%,the MAPE of BP neural network method is 2.8%,and the MAPE of the combined forecasting method is 2.3 %.Therefore the combined forecasting has high precision and practicability.