Mineral　scaling　is　one　of　the　significant　obstacles　in　hypersaline　wastewater　treatment　using　membrane　distillation　(MD)　technology.　A　deeper　understanding　of　the　scaling　mechanism　can　help　to　solve　mineral　scaling　problems.　This　work　investigated　three　porous　membranes　with　different　surface　pore　sizes　and　hydrophobic　properties,　i.e.,　PTFE-0.22,　PTFE-0.10,　and　PVDF-0.22,　used　in　the　direct-contact　membrane　distillation　(DCMD)　process.　We　selected　gypsum　as　a　model　contaminant　in　the　scaling　experiment　and　focused　on　its　homogeneous　and　heterogeneous　nucleation　effects　on　membrane　scaling.　The　morphology　analysis　of　the　scaled　membrane　revealed　that　homogeneous　nucleation　might　be　the　main　reason　for　scaling.　In　addition,　gypsum　crystallization　in　the　membrane　pores　was　the　main　reason　for　the　significant　flux　decline　and　low　physical　cleaning　efficiency　(PTFE-0.22).　When　the　surface　pore　size　of　the　membrane　(PTFE-0.10　and　PVDF-0.22)　was　reduced,　gypsum　crystalization　in　the　pores　could　be　alleviated.　Such　phenomenon　was　mainly　initiated　by　homogeneous　nucleation.　Nonetheless,　the　surface　scaling　was　still　severe　for　PVDF-0.22　because　its　hydrophobicity　was　too　low　to　inhibit　the　heterogeneous　nucleation　on　the　membrane.　However,　PTFE-0.10　with　a　small　surface　pore　size　and　high　hydrophobicity　could　simultaneously　alleviate　the　effect　of　two　nucleations.　We　could　easily　remove　the　gypsum　crystals　deposited　on　the　membrane　surface　by　physical　cleaning　and　achieve　more　than　90%　flux　recovery　efficiency.　Therefore,　reducing　the　surface　pore　size　and　increasing　the　surface　hydrophobicity　should　be　two　main　strategies　in　preparing　the　anti-scaling　hydrophobic　membrane　used　in　MD.