The Y-shaped semi-submersible platform, which is generally composed of three outer columns and one center column that are connected by a Y-shaped pontoon, is the one of the popular foundation concepts for floating wind turbines (FWTs). Because of its non-fully-symmetrical configuration, the directionality effects of ocean climate play a significant role in the dynamic response of the floating system, which indicates that the platform mounting orientation (PMO) should be comprehensively considered before installation at sea. This paper aims at evaluating the importance of PMO from the perspective of lifetime dynamic performance. However, simulating all the short-term conditions from a 25-year met-ocean database is computationally unaffordable. So, limited representative load cases are selected by maximum dissimilarity algorithm and reproduced in FAST, a coupled nonlinear aero-hydro-servo-elastic simulator for FWTs. After calibrating and validating four surrogate models based on 1-year fully simulated results, the Kriging model are adopted to construct lifetime responses. Finally, statistics of five indexes reflect the system performance show that the floating system behaves variously between four PMOs due to the distinct hydrodynamic properties. These findings demonstrate the importance of PMO and provide a guidance for the installation of Y-shaped semisubmersible floating wind turbines. (C) 2020 Elsevier Ltd. All rights reserved.