An accurate and simple compensating method of sloping field have been devised for effective dose planning. The experimental formula, induced with linear absorption coefficient and measured values, shown in formula (5), is applied accurately to sloping compensation of wide region depends on source skin distance, field size, absorption coefficient and angle of incidence. According to this method, the distance of shifting for the normal isodose curve,“h”, is varied by the distance of shifting between the normal and sloping surface,“d”, shown in Fig. 1. We need more simple compensating factor within the permitting error in clinical practice. It is possible to obtain the reasonable compensating factore by analysing the sloping field calculated by the experimental formula. The reasonable compensating factor by analysing the sloping field calculated by the experimental formula. The results of this analysis are shown in Figs. 3-5, comparing with the shift methods of $frac{1}{2}$d. 2/3d and ulcornerd. In radiation therapy it may be recommended to use“Compensating factor”indicated in Table 1 to correct for the sloping field.