Monolayer　transition　metal　dichalcogenides　(ML-TMDCs)　possess　degenerate　levels　with　antiparallel　spins　in　K　and　K′　valleys,　providing　the　intrinsic　valley　polarization,　which　attracts　great　interest　for　potential　applications　on　quantum　information　technology　and　on-chip　nanophotonics.　Unfortunately,　it　is　difficult　to　distinguish　the　degree　of　valley　polarization　(DoP)　near　room　temperature　due　to　the　intensive　phonon-assisted　intervalley　scattering　and　the　long-range　electron-hole　exchange　interaction　in　ML-TMDCs,　limiting　their　practical　applications.　In　this　study,　a　novel　design　is　proposed　for　great　promotion　of　DoP　in　ML-WSe2　with　a　microsphere　cavity　array,　introducing　Purcell　effect　and　nanofocusing　effect　into　the　system.　The　radiative　decay　rate　is　dramatically　enhanced　owing　to　Purcell　effect　in　microcavity　in　weak　coupling　regime,　thus　locking　more　polarized　excitons　in　the　corresponding　valley　under　certain　circularly-polarized　pumping.　In　addition,　the　nanofocusing　effect　contributes　to　increasing　the　number　of　charged　excitons　by　suppressing　the　bright　to　dark　exciton　conversion.　The　present　work　achieves　a　great　DoP　of　ML-WSe2　with　a　simple　configuration　and　promises　broad　applications　from　valleytronic　devices　to　chiral　optics　in　the　future.　©　2023　Wiley-VCH　GmbH.