The　effect　of　local　site　conditions　on　the　earthquake　ground　motion　is　a　very　important　factor　to　be　considered　in　engineering　seismic　fortification.　Many　methods,　such　as　numerical　simulation　methods　based　on　site　analysis　models　and　statistical　empirical　relation　methods　based　on　the　earthquake　ground　motion　observations　and　numerical　simulation　data,　have　been　used　to　consider　the　site　effects　in　actual　engineering　seismic　fortification　and　earthquake　disaster　assessment.　The　statistical　analysis　to　obtain　characteristic　parameters　of　site　condition　effect　based　on　strong　motion　and　microtremor　records　become　an　economical　and　practical　method　of　determining　the　designed　ground　motion　of　engineering　sites,　especially　for　large　survey　areas　and　engineering　sites　where　it　is　difficult　to　carry　out　a　site　survey.　In　this　paper,　a　novel　evaluation　method　for　site　effect　on　earthquake　ground　motion　is　proposed.　The　new　method　is　based　on　the　horizontal　to　vertical　spectral　ratio　(HVSR)　method,　but　the　original　HVSR　is　replaced　by　a　modified　HVSR　considering　the　effect　of　the　soil　layer　on　the　vertical　ground　motion.　In　order　to　build　the　model　and　determine　the　corresponding　parameters　of　the　modified　HVSR,　first,　the　ground　motions　in　the　bedrock　below　the　soil　layer　are　calculated　using　the　one-dimensional　equivalent　linear　method.　These　calculated　records　are　independent　of　the　influence　of　the　downgoing　wavefield,　and　the　differences　between　the　ground　surface　to　bedrock　spectral　ratio　(SBSR).　The　HVSR　for　the　local　sites　of　ground　motion　observation　stations　are　analyzed　using　the　strong　ground　motion　records　from　the　Kiban-Kyoshin　network　(KiK-net)　in　Japan.　The　statistical　characteristics　of　the　relationship　between　SBSR　and　HVSR　are　revealed,　and　then,　a　quantitative　relationship　between　SBSR/HVSR　and　HVSR　is　established.　The　proposed　evaluation　method　for　the　site　effect　has　the　advantage　that　the　original　HVSR　method　only　requires　ground　motion　records　on　the　ground　surface　of　the　site,　and　it　further　considers　the　influence　of　the　vertical　seismic　effect　on　the　accuracy　of　the　HVSR　method.　The　proposed　method　can　characterize　the　influence　of　the　site　conditions　on　ground　motion　more　reasonably　than　the　conventional　method.