It＇s　not　easy　to　build　a　mathematic　model　for　the　complex　structures,　such　as　ancient　towers.　Compared　with　forced　vibration　tests,　the　ambient　vibration　test　is　more　convenient　and　it　has　enough　accuracy　for　the　small　amplitude　response　characteristics.　In　this　paper,　the　method　of　ambient　vibration　test　is　applied　for　measuring　a　wood　tower　in　Ying　County,　Shanxi,China.　In　the　frequency　domain,　the　method　of　random　signal　data　analysis　is　performed　to　obtain　the　natural　frequencies.　Then　the　mode　shapes　of　the　wood　tower　are　determined　based　on　the　mode　amplitudes　at　each　observation　point　and　zero　delayed　cross-correlation　function.　Finally,　the　damping　ratio　of　each　mode　is　calculated　by　using　the　half　-　power　point　method　on　the　basis　of　auto　power　spectrum　and　cross　power　spectrum.　The　results　show　that　the　vibration　characteristics　of　the　tower　in　two　horizontal　directions　are　slightly　distinct,　and　the　damping　ratio　of　the　first　mode　is　greater　than　that　of　the　second　mode.