A new product development cost estimation method is proposed on the base of grey model and BP neural network model to improve the precision of estimation result in this paper. Although grey model and BP neural network model are good methods for the new product development cost estimation, there are inevitably limitations for any single model. The paper uses optimal weight combination method to integrate the results of the grey model and BP neural network model.This integration makes a better result than any single model with the minimum error square sum and improves the accuracy of estimation.