Background　Nationwide　studies　that　examine　climatic　modification　effects　on　the　association　between　air　pollution　and　health　outcome　are　limited　in　developing　countries.　Moreover,　few　studies　focus　on　PM1　pollution　despite　its　greater　health　effect.　Objectives　This　study　aims　to　determine　the　modification　effects　of　climatic　factors　on　the　associations　between　PM1　and　the　incidence　rates　of　lung　cancer　for　males　and　females　in　China.　Methods　We　conducted　a　nationwide　analysis　in　345　Chinese　counties　(districts)　from　2014　to　2015.　Mean　air　temperature　and　relative　humidity　over　the　study　period　were　used　as　the　proxies　of　climatic　conditions.　In　terms　of　the　multivariable　linear　regression　model,　we　examined　climatic　modification　effects　in　the　stratified　and　combined　datasets　according　to　the　three-category　and　binary　divisions　of　climatic　factors.　Moreover,　we　performed　three　sensitivity　analyses　to　test　the　robustness　of　climatic　modification　effects.　Results　We　found　a　stronger　association　between　PM1　and　the　incidence　rate　of　male　lung　cancer　in　counties　with　high　levels　of　air　temperature　or　relative　humidity.　If　there　is　a　10　mu　g/m(3)　shift　in　PM1,　then　the　change　in　male　incidence　rate　relative　to　its　mean　was　higher　by　4.39%　(95%　CI:　2.19,　6.58%)　and　8.37%　(95%　CI:　5.18,　11.56%)　in　the　middle　and　high　temperature　groups　than　in　the　low　temperature　group,　respectively.　The　findings　of　climatic　modification　effects　were　robust　in　the　three　sensitivity　analyses.　No　significant　modification　effect　was　discovered　for　female　incidence　rate.　Conclusions　Male　residents　in　high　temperature　or　humidity　counties　suffer　from　a　larger　effect　of　PM1　on　the　incidence　rate　of　lung　cancer　in　China.　Future　research　on　air　pollution-related　health　impact　assessment　should　consider　the　differential　air　pollution　effects　across　different　climatic　conditions.