The O-cell pile testing(OPT) method is a new axial static load test of pile. Based on plastic law of pile lateral soil，a set of analytical equations of the loading-settlement curve for OPT are established by using load transfer method，in which pile lateral soil is simulated with bilinear load-transfer model and pile toe soil with trilinear load-transfer model. The method to get the parameter of the load-transfer function is discussed. The analytical equation verified by two history engineering cases can be used to describe the loading-settlement characteristic of OPT effectively.