Based on the measured data of six field test piles in Quanzhou downtown area,the optimizing fit analysis was conducted on the pile cap displacement curve of up drag for PHC Pile.Through software platform 1stOp,Levenberg-Marquardt was first combined with Universal Global Optimization-UGO as the fitting method;then the six field test piles were fitted by means of hyperbolic curve model, power function model and compound model of hyperbolic curve power function.The results showed that the fitting accuracy of compound model of hyperbolic curve power function was the highest,and all its correlation coefficient R was above 0.9999.Besides,such model had a better fitting effect on the uplift of PHC Pile than that of hyperbolic curve model and power function model.Generally,the error of calculated value and measured value for up drag of PHC Pile grounded on the mathematic model was between-0.48% and 0.55%.Yet compared with the value 1400kN of ultimate vertical uplift bearing capacity of a single pile from the test report,together with the predicted result according to the fitting curve,the result was more or less improved with the highest value 59.13%.Thus,the pile cap displacement curve of up drag for PHC Pile was fitted via the compound model of hyperbolic curve power function and the prediction was conducted on ultimate vertical uplift bearing capacity of a single pile,the result of which is relatively accurate and reliable.