HsinYi area is rapidly developing political and economic zone in these days, the opening of Taipei Financial Center has made this neighborhood a well-known new spot internationally. But from many earthquake damage records, this area is much more serious than epicenter that are far from hundred kilometers as Hualien and Ilan. Scrutiny the two stations of strong motion network in HsinYi（TAP022 and TAP089）we discover that TAP022（close Taipei Financial Center） receives more earthquake datas than TAP089, its recording intensity is also more large, but the trigger level of the two strong motion stations are the same.We use the common earthquake datas of the two stations and very intensive microtremor measurement in HsinYi area to investigate and discuss the site effect of the two stations especially. Then compare our site effect map with and SunShan thickness and velocity maps for discussing the ground motion characters of the two sites and their possible reasons.We fine that using microtremor measurement can get a well fit in site effect and SunShan thickness maps；and we make sure that SunShan thickness controls the site TAP022’s low frequency（1∼2Hz）site effect, no matter what the earthquake’s energy pass this area, the horizontal component will enlarge especially about 1Hz.This research also verifies that using microtremor measurement is a good geophysical method for estimating the site effect of alluvium. By the way we can apply those site effect estimation for seismic hazard analysis.
