The　reference　evapotranspiration　(ET0)　has　decreased　over　most　of　China　under　climate　change　over　the　past　few　decades,　especially　before　the　1990s,　which　significantly　affects　the　agricultural　water　requirements.　In　this　study,　the　recent　tendency　of　ET0　over　China　was　determined　and　the　issues　of　what　causes　this　tendency　and　how　this　tendency　would　affect　agricultural　water　demand　were　discussed.　First,　we　evaluate　ET0　(consisting　of　the　aerodynamic　term　ET0_a　and　the　radiative　term　ET(0_)r)　using　the　Penman-Monteith　method　based　on　the　grid-based　China　Meteorological　Forcing　Dataset　(CMFD)　from　1979　to　2015.　Second,　we　analyze　the　trends　of　ET0　and　five　climatic　variables　using　the　Mann-Kendall　test　and　the　Sen＇s　slope　estimator.　Finally,　we　assess　the　impacts　of　meteorological　factors　on　ET0　by　calculating　dimensionless　sensitivity　coefficients　and　contribution　rates.　Based　on　the　ET0　results　and　precipitation　data,　we　also　evaluate　the　aridity　index　(AI)　over　China　to　explore　the　impacts　of　the　tendency　of　ET0.　The　result　of　the　trend　analysis　of　ET0　reveals　that　there　is　a　significantly　increasing　trend　after　the　1990s　over　China,　and　this　trend　could　be　attributed　to　the　increasing　air　temperature　based　on　the　results　of　the　contribution　rates,　where　ET0　is　most　sensitive　to　the　specific　humidity.　The　AI　result　reveals　a　decreasing　trend　over　the　study　period,　which　indicates　that　the　irrigation　water　supply　could　be　appropriately　reduced　on　the　premise　of　proper　and　scientific　utilization　of　water　due　to　the　more　significantly　increasing　availability　of　water　even　though　the　water　demand　for　evapotranspiration　increased.