Layer-structured　transition　metal　dichalcogenides　(LS-TMDs)　are　being　heavily　studied　in　K-ion　batteries　(KIBs)　owing　to　their　structural　uniqueness　and　interesting　electrochemical　mechanisms.　Synthetic　methods　are　designed　primarily　focusing　on　high　capacities.　The　achieved　performance　is　often　the　collective　results　of　several　contributing　factors.　It　is　important　to　decouple　the　factors　and　understand　their　functions　individually.　This　work　presents　a　study　focusing　on　an　individual　factor,　crystallinity,　by　taking　MoS2　as　a　demonstrator.　The　performance　of　low　and　high-crystallized　MoS2　is　compared　to　show　the　function　of　crystallinity　is　dependent　on　the　electrochemical　mechanism.　Lower　crystallinity　can　alleviate　diffusional　limitation　in　0.5-3.0　V,　where　intercalation　reaction　takes　charge　in　storing　K-ions.　Higher　crystallinity　can　ensure　the　structural　stability　of　the　MoS2　layers　and　promote　surface　charge　storage　in　0.01-3.0　V,　where　conversion　reaction　mainly　contributes.　The　low-crystallized　MoS2　exhibits　an　intercalation　capacity　(118　mAh　g(-1)),　good　cyclability　(85%　over　100　cycles),　and　great　rate　capability　(41　mAh　g(-1)　at　2　A　g(-1)),　and　the　high-crystallized　MoS2　delivers　a　high　capacity　of　330　mAh　g(-1)　at　1　A　g(-1)　and　retains　161　mAh　g(-1)　at　20　A　g(-1),　being　one　of　the　best　among　the　reported　LS-TMDs　in　KIBs.