Election　and　voting　play　crucial　roles　in　democratic　society　for　an　elactorate　to　make　a　collective　decision.　E-voting　is　one　of　the　most　challenging　problems　in　cryptographic　research　to　provide　multiple　dimensions　security　assurances.　In　this　paper,　we　study　an　important　voting　paradigm,　score　voting,　with　privacy　protection,　which　has　not　been　investigated　in　previous　work.　We　propose　a　blockchain　based　self-tallying　election　system　to　support　score　voting,　dubbed　＂PriScore＂,　where　the　ballots　are　recorded　on　blockchain　to　prevent　vote　forgery　or　tampering.　PriScore　makes　it　possible　for　each　voter　to　assign　different　evaluation　scores　(within　a　certain　range)　for　the　candidates　as　ranked-choice,　where　the　sum　of　the　scores　in　each　ballot　should　be　a　predefined　constant,　and　the　evaluation　scores　are　encrypted　to　maintain　confidentiality.　A　major　challenge　in　score　voting　is　to　simultaneously　prove　two　constraint　conditions:　range　proof　and　sum　proof.　We　introduce　a　new　technique,　called　dual　zero-knowledge　proof　(dual-ZKP),　to　prove　the　scores　satisfying　two　crucial　requirements,　which　integrates　＂1-out-of-K＂　proof　and　distributed　ElGamal　crypto　in　a　non-trivial　way.　The　self-tallying　mechanism　in　PriScore　enables　any　party　in　the　system　to　calculate　and　verify　the　election　result,　which　provides　fairness,　dispute-freeness.　The　security　analysis　demonstrates　that　PriScore　achieves　completeness,　soundness,　eligibility,　universal/individual　verifiability　and　multiple-voting　detection.　We　evaluate　the　performance　of　PriScore　on　modern　workbench　to　test　the　performance,　and　also　on　a　blockchain　platform　to　measure　the　resource　consumption.　The　experiments　show　that　PriScore　preserves　privacy　of　score　voting　with　reasonable　overheads.