The　proper　use　of　medical　data　plays　a　vital　role　in　the　development　of　medical　research.　However,　there　are　challenges　related　to　privacy　leakage　in　medical　data　sharing　and　the　controllability　of　data　by　patients　during　its　use.　To　address　these　issues,　this　study　proposes　a　blockchain-based　scheme　for　controlling　access　to　medical　data.　Firstly,　a　medical　data　sharing　scheme　based　on　blockchain　is　constructed,　incorporating　a　medical　data　sharing　scheme　based　on　proxy　re-encryption.　This　solution　achieves　secure　sharing　of　medical　data　while　protecting　the　privacy　and　security　of　patient　medical　data　through　proxy　re-encryption　technology,　with　consensus　nodes　acting　as　proxy　nodes　responsible　for　proxy　re-encryption.　Secondly,　a　mechanism　for　dynamically　adjusting　data　access　permissions　is　designed.　Access　control　policies　are　stored　in　smart　contracts,　allowing　patients　to　interact　with　smart　contracts　to　update　medical　data　access　permissions　by　modifying　attribute　lists,　thereby　achieving　controllable　sharing　of　medical　data　by　patients.　Finally,　security　analysis　indicates　that　the　proposed　scheme　can　protect　medical　data　privacy,　enable　dynamic　data　sharing,　and　resist　collusion　attacks.　Performance　analysis　shows　that　the　scheme　has　advantages　in　terms　of　communication　overhead　and　computational　costs,　making　it　suitable　for　controlled　data　sharing　between　patients　or　hospitals　and　research　institutions.　©　2024　SPIE.