Among several wind farm layout design parameters, the inter-turbine spacing, which has a great influence on aerodynamic power output, wind speed deficit, lifetime, wake vortex structure, is one of the most critical factors. Therefore, the effects of inter-turbine spacing on aerodynamics for wind farms must be carefully studied. In this study, Considering the uniform inflow conditions, the effects of inter-turbine spacing changing from three to nine times of rotor diameter on aerodynamics for wind farms containing two NREL 5MW baseline wind turbines in tandem layout are analyzed using actuator line model and CFD method, and the RANS equation with k-ω SST turbulence model was solved in the simulations conducted in the OpenFOAM. From the study, it is concluded that the inter-turbine spacing has significant effects on the aerodynamic power and wake characteristics. The aerodynamic power output of the downstream wind turbine exits sharp fluctuation before power output of the downstream wind turbine is becoming steady. Furthermore, periodic oscillation whose period is about the one-third of rotor rotating period can be also concluded from the study. Moreover, there is strong wake interaction which will impact the aerodynamics for wind farms seriously.