In the re-pressed tests of jacked pipe piles in soft clay, it was observed that the re-pressed starting pressure can reach to more than 2.5 times of the final pressure for 25 days after finishing the installation; and it increased more rapidly in early period than later. Through the study of the time effect mechanism, it is found that the increment of ultimate bearing capacity of the single pile is mainly caused by side soil resistance. The end resistance has little influence on the time effect of bearing capacity of pile. According to the simulation result of the test data, the relationship between pile side resistance and time can be described with logarithmic curve. By this new computing model, the side frictional resistance in different resting time can be obtained, and then the ultimate bearing capacity. It is proved that this method is feasible because the values of side soil resistance calculated by the computing model with software are well consistent with the field tests results.