This paper explores the possibility of improving the accuracy for the 2-dimentional effective analysis code FLIP for open-type wharves on vertical piles. We picked up both the damaged and no-damaged wharves by 1995 Hyogoken Nambu earthquake as study subjects. Through this study, the following conclusions are drawn. 1) The analysis results of damaged T-wharf indicated that the adequate proportional coefficient of the pile-ground interaction spring (PFACT) is 1.0 and while it is better to be less than 1.0 near the ground surface. 2) The analysis results of no-damaged N-wharf indicated that the accurate simulation of the deformation of the earth retaining wall is important to predict the steel piles stress resultants. The reduction of PFACT near the ground surface has a minor influence on the analysis in the case of small ground deformation around the steel piles.