Recent developments in wind turbine design research account for the effects of velocity fluctuation and the characteristic turbulence of the installation location site to improve performance. For the design, a low-cost natural wind generator and a laboratory-based performance evaluation of the wind turbine are useful. This paper describes a new actively controlled multi-fan wind tunnel that generates natural wind at a reduced cost. The driving section of its wind tunnel has 100 PC cooling fans that are controlled by an original embedded system. The fluctuating velocity wind is successfully generated with a mean velocity 7m/s, turbulent intensity 2% and turbulent integral scale 5 m, 10 m, 20 m, based on Karman’s power spectrum density function. In particular, the wind satisfies the Kolmogorov’s −5/3 multiplication rule of inertial subrange with the frequency range 0.01∼2.0 Hz. Furthermore, the performance of a wind turbine in steady and natural winds can be investigated. From the results, it is made clear that integral scale has a large effect on the wind turbine performance. The maximum power coefficient in natural wind of the integral scale 5 m and 10m is 124% larger than one of steady wind with the same mean velocity 7 m/s.