A　research　on　acid　precipitation　and　rainwater　chemical　composition　in　a　town,　close　to　large　city,　was　performed　in　Yongchuan,　southwest　China.　The　precipitation　was　typically　acidic　and　the　volume-weighted　mean　(VWM)　value　of　pH　is　5.04.　The　VWM　equivalent　concentration　of　samples　components　followed　in　order　of　SO42-,　NH4+,　Ca2+,　H+,　Cl-,　K+,　Mg2+,　Na+,　NO3-　and　PO43-.　The　ions　of　SO42-,　NH4+,　Ca2+,　H+　and　Cl-　in　rainwater　accounted　for　88.7%　of　the　total　ions　and　SO42-　is　the　primary　cause　of　acid　rain.　NH4+　and　Ca2+　were　the　main　neutralizing　constituents　according　to　calculated　neutralization　factors.　The　enrichment　factor　shows　that　SO42-　and　NO3-　mainly　originated　from　anthropogenic　activities.　NH4+　might　come　from　agricultural　activities.　Cl-　plausibly　came　from　marine　sources.　Ca2+,　Mg2+　and　K+　could　primarily　resulted　from　soil.　Significant　correlations　(P＜0.01)　were　found　among　SO42-,　NH4+,　NO3-　and　COD　reflect　these　ions　shared　common　sources　such　as　coal　combustion,　industrial　discharge　and　evaporation　chemical　fertilizer.　Forest　planting,　minimizing　the　discharge　of　sulfurous　pollutants,　reducing　emissions　from　cars　and　searching　sustainable　new　energy　sources　to　replace　fossil　fuels　could　prevent　and　limit　the　spread　of　acid　rain.