This　paper　aims　to　quantitatively　study　the　impact　of　backfill　and　foundation　pits　on　free-field　ground　motion.　A　finite　element　model　for　this　issue　is　established　based　on　the　actual　situation.　Using　the　numerical　simulation　method　of　the　concentrated　mass　explicit　dynamic　finite　element,　we　analyze　the　effects　of　the　shear　wave　velocity,　the　thickness　of　backfill　soil,　and　the　size　of　foundation　pit　on　free-field　ground　motion.　At　the　same　time,　the　remodeling　soil　analysis　models　are　established　to　analyze　the　effect　of　remolded　soil　on　free-field　ground　motion.　The　results　show　that　both　the　backfill　soil　and　foundation　pits　can　affect　the　free-field　ground　motion　peaks　and　the　values　of　response　spectrum　significantly.　With　the　increase　of　the　thickness　of　backfill　soil　and　the　depth　of　foundation　pits,　the　influence　is　more　noticeable.　Replacing　the　backfill　by　remolding　soil　can　reduce　the　effect　of　the　backfill　on　the　free　field.　The　results　can　provide　a　basis　for　the　rational　use　of　the　strong　ground　motion　records　on　the　backfill　site　and　the　construction　of　the　strong　ground　motion　observation　stations.