There is radiation effect among power loads in adjacent regions. The radiation effect is obvious among commercial load and residential load. It is less obvious among industrial loads， with more randomization. A new method is proposed， which takes radiation effect among power loads into consideration referring to scalar field. The new method is applied in long-term load forecasting. Firstly， the saturate load of each area is predicted through load-density method. Then， the loads are adjusted as taking radiation effect into account. After adjustment， the result would be close to practical situation. The method has been employed in Zhongshan Power Supply Bureau. Through case study and application， the validity of the method is proved.