The natural period is generally used for monitoring the change in structural dynamic characteristics. It is legally obligated in Korea that seismic acceleration measurement system is installed in structures and measured data are transmitted. However there are some difficulties that the natural period is automatically analyzed by the structural acceleration analysis system. First, structural characteristics is changed by various factor such as plan shape, foundation type, structure type, size, and so on. Second, there are many factors ― machinery(basement), conditioning equipment(roof) ― causing noises near the measurement system installation point. Lastly, there are only sent some interval data by earthquake except ambient vibration to the analysis system. In this study to estimate the natural period, systemic approach is developed using simple evaluation formula from Korean Building Code-2009(KBC-2009).