In　proof-of-work　(PoW)-based　blockchain　network,　the　blockchain　miners　publish　blocks　by　contributing　computing　power　to　solve　crypto-puzzles.　Due　to　the　weak　computing　power　of　single　miner,　miners　tend　to　join　a　mining　pool　and　share　the　profits　from　the　mining　pool　according　to　the　contribution　proportions　of　the　miners.　However,　some　miners　may　initiate　block　withholding　attack　which　may　result　in　wasting　computing　power,　even　threatening　the　efficiency　of　the　blockchain　network.　To　address　this　problem,　in　this　paper,　we　use　the　biform　game　model　to　optimize　the　miners’　strategy　choices.　We　firstly　formulate　the　mining　process　as　a　non-cooperative–cooperative　biform　game　model.　We　use　the　model　to　exhibit　miners’　strategy　choices　(non-cooperation　stage)　and　the　cooperation　mining　process　(cooperation　stage).　Then　we　set　the　conditions　to　maintain　the　voluntary　honest　behavior　of　miners.　After　that,　we　employ　the　semi-CIS　(semi-the　center　of　imputation　set　value)　value　to　compute　the　solutions　of　the　cooperative　games　in　the　cooperation　stage,　and　optimize　miners’　strategy　choices　to　prevent　the　block　withholding　attack.　Hence　we　can　ensure　the　blockchain　network　is　secure.　Finally,　the　validity　and　applicability　of　the　proposed　model　and　method　are　verified　by　a　numerical　example.　©　2019　The　Authors.　Published　by　Atlantis　Press　SARL.