Abstract: The heteroscedasticity are usually considered in applying the Weighted Least Squares (WLS) method, and it has a wide range of applications in economic forecast. A cost forecasting model was put forward using WLS me thod, which was based on a combination of studies on the batch manufacturing practice of weaponry and relevant econometric theory. The results of analyses by this model show that it can eliminate the impact of heterosc edasticity on the forecast works, and achieve a better forecast and fit of model than common WLS method.