We report a new search for weakly interacting massive particles ( WIMPs ) using the combined low background data sets acquired in 2016 and 2017 from the PandaX-II experiment in China .
The latest data set contains a new exposure of 77.1 live day , with the background reduced to a level of 0.8 \times 10 ^ { -3 } evt/kg/day , improved by a factor of 2.5 in comparison to the previous run in 2016 .
No excess events were found above the expected background .
With a total exposure of 5.4 \times 10 ^ { 4 } kg day , the most stringent upper limit on spin-independent WIMP-nucleon cross section was set for a WIMP with mass larger than 100 GeV/ c ^ { 2 } , with the lowest 90 % C.L .
exclusion at 8.6 \times 10 ^ { -47 } cm ^ { 2 } at 40 GeV/ c ^ { 2 } .