Up flow wind is a distinctive feature in complex terrains. By reason of the differences of tilt angles, downwind turbines have smaller misalignments toward up flow wind than upwind turbines. It makes the former generates more power than the latter in complex terrains. The advantage of downwind turbines was demonstrated in field tests using a same turbine in both rotor positions. Performance improvements were measured as much as +5 to +20% in +1 to +11deg of inclinations. Wind simulation of a wind farm in a typical complex terrain was also carried out. It shows annual energy averaged inclination is +7.5deg, where time average inclination is +6.0deg. And 7.6% more AEP was calculated by downwind turbines as compared with upwind turbines.