Recently, the piled raft foundation has been widely applied in Vietnam. Determination of suitable pile stiffness is one of the most important problem in the piled raft foundation design. This paper presents the analysis and comparison of methods for calculating the pile stiffness. The analytical calculation methods and experimental methods are used to study the pile stiffness. Results of analytical method are compared each other and with the results of the pile load test which is considered as an accuracy method. Research results on the pile stiff-ness show that Tsutovic method gives results that are closest to the results of pile load tests in the field (from 9.5% to 23.7%), this difference margin is smaller than the other methods. Therefore, this is the recommended method when calculating the pile stiffness. The recommended average difference coefficient between the above two methods has been proposed. Then, it is possible to predict the pile stiffness according to the pile load tests in the field based on the results of Tsutovic method. In addition, in the simulations of piled raft foundation using the finite element method, no matter how large or small the cross-section of a pile is, the pile is usually simulated by one spring in the calculation model. This simulation is not reasonable because it ignores the cross-sectional size of the pile. This does not reflect the nature of the actual working process of piled raft foundations. With large projects, the difference can be significant. To provide a reasonable method when simulating piles using the finite element method, this study conducted simulations of large diameter piles using different options for evaluation and analysis. From the studied results, the conclusions and the proposals are presented for the pile stiffness determinations.