A　study　of　seismic　failure　mechanism　of　soft　soil　sites　in　Fuzhou　is　presented.　The　characteristics　of　frequency-spectrum　structure　and　response　of　ground　soils,　including　soft　soils　and　the　frequency　of　ground　micro-tremor,　were　investigated.　From　the　results,　it　is　found　that　the　site　soft　soil　enlarges　predominant　period　of　ground　micro-tremor　to　some　degree,　and　the　predominant　period　of　ground　micro-tremor　has　a　close　relationship　with　the　stiffness　of　the　foundation　soils.　The　correlations　among　the　predominant　period　of　ground　micro-tremor,　the　overburden　thickness　of　soils,　and　the　shear　wave　velocity　of　overburden,　are　established.　These　relations　reveal　that　the　predominant　period　of　the　ground　micro-tremor　is　positively　proportional　to　overburden　thickness,　but　decreases　with　the　increase　of　shear　wave　velocity.　In　addition,　based　on　the　completed　measurements　of　the　natural　periods　of　the　buildings　in　the　city,　using　the　empirical　calculation　methods,　and　approximate　calculation　methods　applied　in　California,　USA,　the　improved　approximate　calculation　formulae　are　developed　for　natural　periods　of　high-rise　buildings.　The　results　reveal　the　seismic　failure　mechanism　in　the　abundant　soft　soil　sites,　and　demonstrate　the　causes　of　potential　seismic　failures　for　some　buildings.