Objective:　To　explore　the　influence　of　the　blood　flow-diameter　scaling　laws　of　Q　alpha　D-3,　Q　alpha　D-2.7　and　Q　alpha　D-7/3　on　the　numerical　simulation　of　fraction　flow　reserve　based　on　CTA　images　and　to　find　the　optimal　exponents.　Methods:　1)　26　patients　with　coronary　artery　disease　were　screened　according　to　the　inclusion　criteria;　2)　Microcirculation　resistance　(R-m)　was　calculated　under　the　3,　2.7　and　7/3　power　of　the　flow-diameter　scaling　law,　which　were　recorded　as　3R(m),　2.7R(m)　and　7/3R(m),　respectively;　3)　3R(m),　2.7R(m)　and　7/3R(m)　were　used　as　exit　boundary　conditions　to　simulate　FFRCT,　quoted　as　3FFRCT,　2.7FFRCT　and　7/3FFRCT,　respectively;　4)　The　correlation　and　diagnostic　performance　between　three　kinds　of　FFRCT　and　FFR　were　analyzed.　Results:　The　p-values　of　comparing　3Rm,　2.7Rm　and　7/3Rm　with　FFR　were　0.004,　0.005　and　0.010,　respectively;　the　r　value　between　7/3FFRCT　and　FFR　(0.96)　was　better　than　that　of　3FFRCT　(0.95)　and　2.7FFRCT　(0.95);　the　95%　LoA　between　7/3FFRCT　and　FFR　(-0.08　similar　to　0.11)　was　smaller　than　that　of　3FFRCT　(-0.10　similar　to　0.12)　and　2.7FFRCT　(-0.09　similar　to　0.11);　the　AUC　and　accuracy　of　7/3FFRCT　[0.962　(0.805-0.999),　96.15%]　were　the　same　as　those　of　2.7FFRCT　[0.962　(0.805-0.999),　96.15%]　and　better　than　those　of　3FFRCT　[0.944　(0.777-0.996),　92.3%].　The　prediction　threshold　of　7/3FFRCT　(0.791)　was　closer　to　0.8　than　that　of　3FFRCT　(0.816)　and　2.7FFRCT　(0.787).　Conclusion:　The　blood　flow-diameter　scaling　law　affects　the　FFRCT　simulation　by　influencing　the　exit　boundary　condition　R-m　of　the　calculation.　With　Q　alpha　D-7/3,　FFRCT　had　the　highest　diagnostic　performance.　The　blood　flow-diameter　scaling　law　provides　theoretical　support　for　the　blood　flow　distribution　in　the　bifurcated　vessel　and　improves　the　FFRCT　model.