The wake interaction between floating offshore wind turbines (FOWTs) has a significant effect on the FOWT's power output, system dynamics responses and structural loadings. To better understand the wake interaction phenomenon in floating wind farms, fully coupled simulations considering the coupling effects between the wind turbine, floating platform and mooring system for FOWTs are necessary. In the present paper, the unsteady actuator line model (UALM) is embedded into in-house CFD solver naoe-FOAM-SJTU to establish a fully coupled CFD analysis tool named FOWT-UALM-SJTU for numerical simulations of FOWTs. Coupled aero-hydrodynamic simulations of two OC3 Hywindspar FOWT models in tandem layout under shear wind and regular wave conditions are performed using this tool. The unsteady aerodynamics of wind turbines are given by the UALM, and the hydrodynamic responses of floating platforms and mooring tensions are predicted by naoe-FOAM-SJTU. From the simulations, unsteady aerodynamic characteristics can be extracted including the rotor power and thrust as well as detailed wake flow information, and hydrodynamic responses such as the six-degree-of-freedom motions and mooring tensions are also available. Moreover, the influence of wake interaction on the performance of FOWTs is studied. It can be found that strong wake interaction phenomenon is observed and the unsteady aero-hydrodynamic responses of downstream FOWT system are greatly affected by the wake interaction.