In　order　to　confirm　which　process　is　the　most　important　in　the　blood　coagulation　cascade,　a　dynamic　model　on　the　function　of　platelets　in　blood　coagulation　is　presented　based　on　biochemical　experiments.　Based　on　qualitative　analysis　and　mathematical　simulation,　a　series　of　conclusions　about　the　influence　of　the　activation　rate　of　factor　VIII　and　factor　IX　on　the　generation　of　thrombin　(IIa)　are　drawn.　It　is　evident　that　the　pro-coagulation　stimulus　must　exceed　a　threshold　value　to　initiate　the　coagulation　cascade.　The　value　is　related　to　the　binding　constant　d2　of　the　platelet.　The　stability　of　the　equilibrium　value　is　also　related　to　the　pro-coagulation　stimulus.　This　article　also　evaluates　the　influence　of　the　stimulus　strength　and　the　activated　rate　parameter　of　platelets　on　thrombin.　The　proportion　of　platelets　activated　at　any　given　time　is　designated　c.　To　each　c,　we　obtain　a　maximum　concentration　of　thrombin.　It　is　evident　that　when　the　level　of　factor　IX　is　below　1%　of　the　normal　level,　the　rate　of　thrombin　generation　reduces　dramatically,　resulting　in　severe　bleeding　tendency.