For judging the security of pile foundation, the loading static test is popularly used in engineering. Some conditions could confine this method to estimate the ultimately loading according with objectivity, for example the high loading bearing pile foundation, the especial condition of static test, over length pile, etc.. So the strength reduction method (SRM) is put research this question in the basis of the ultimate loading capacity theory of pile foundation and the limit analysis of FEM. The judging condition and the safety storage factor (SSF) of SRM were built. The judging condition have three item, (1) the inflexion lies on F-s curve, and the bottom of F-s curve is parallel to the s axis; (2) the point of V type appear on F-Qu curve, so the previous reduction factor of this inflexion of F-s curve and the point of V type of F-Qu curve is SSF on the loading condition of pile head; (3) the equivalent plastic strain connected in soils around pile shaft and pile end. This method was used to analyze and estimate the ultimately loading of the large diameter pile, and its error of SRM to the static loading test and the increment loading method of FEM (ILM) are less 5%. So it shown that SRM may be used to attempt in engineering for judging the security of pile foundation and computing the ultimately loading.