Objective:　To　calculate　fractional　flow　reserve　(FFR)　based　on　computed　tomography　angiography　(i.e.,　FFRCT)　by　considering　the　branch　flow　distribution　in　the　coronary　arteries.　Background:　FFR　is　the　gold　standard　to　diagnose　myocardial　ischemia　caused　by　coronary　stenosis.　An　accurate　and　noninvasive　method　for　obtaining　total　coronary　blood　flow　is　needed　for　the　calculation　of　FFRCT.　Methods:　A　mathematical　model　for　estimating　the　coronary　blood　flow　rate　and　two　approaches　for　setting　the　patient-specific　flow　boundary　condition　were　proposed.　Coronary　branch　flow　distribution　methods　based　on　a　volume-flow　approach　and　a　diameter-flow　approach　were　employed　for　the　numerical　simulation　of　FFRCT.　The　values　of　simulated　FFR(CT　)for　16　patients　were　compared　with　their　clinically　measured　FFR.　Results:　The　ratio　of　total　coronary　blood　flow　to　cardiac　output　and　the　myocardial　blood　flow　under　the　condition　of　hyperemia　were　16.97%　and　4.07　mL/min/g,　respectively.　The　errors　of　FFRCT　compared　with　clinical　data　under　the　volume-flow　approach　and　diameter-flow　approach　were　10.47%　and　11.76%,　respectively,　the　diagnostic　accuracies　of　FFR(CT　)were　65%　and　85%,　and　the　consistencies　were　95%　and　90%.　Conclusions:　The　mathematical　model　for　estimating　the　coronary　blood　flow　rate　and　the　coronary　branch　flow　distribution　method　can　be　applied　to　calculate　the　value　of　clinical　noninvasive　FFRCT.