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Background: Tandem stenoses were widely observed in acute stroke cases. High pressure drop and low fractional flow (FF) indicate the risk of ischemia caused by intracranial atherosclerotic stenosis. Low wall shear stress (WSS) and high low-density lipoprotein (LDL) filtration rate indicate the risk of atherosclerotic plaque growth. High WSS is related to the risk of plaque rupture. The hemodynamic parameters (pressure drop, FF, WSS, and LDL filtration rate) could be estimated using computational fluid dynamics (CFD) simulation. Few studies have investigated the hemodynamics of intracranial tandem stenoses. This study aims to estimate the clinical risks of intracranial tandem stenoses using CFD simulation.Methods: With identical radius and length, 4 cylindrical tube models were developed with different stenoses (severity in area: 75% single, 75%-84% tandem, 75%-84%-89% tandem, and 89% single). The pressure drop and FF of each stenosis were derived from static CFD simulation and compared between models. A transient CFD simulation was performed on a patient-specific intracranial arterial model with three (56.2%, 51.3%, and 89.8%) tandem stenoses using boundary conditions derived from patient-specific measurements. For the three stenoses, pressure drop, FF, WSS, and LDL filtration rate were calculated and compared.Results: Independent from other stenoses, 89% single stenosis caused comparable pressure drops in four tube models (difference less than 10%), larger than those of 75%-84% tandem stenoses. 89% stenosis had the lowest FF (less than 0.85). In the patient-specific model, the 56.2% and 51.3% stenoses had pressure drops less than 2mmHg with FFs higher than 0.98, while the 89.8% stenosis caused a pressure drop more than 10mmHg with FF lower than 0.90, where a high WSS belt extended distally. Compared with low WSS (less than 0.5Pa), high LDL filtration rate appeared in smaller areas on arterial wall, with less temporal fluctuations.Conclusions: 1. Tandem stenoses are independent in pressure drop and FF. Pressure drop increases sharply with the severity of stenosis. 2. Compared with low WSS, high LDL filtration rate is more specific and stable in reflecting the risk of intracranial atherosclerotic plaque growth. 3. The risks of both plaque growth and rupture should be considered in severe stenoses.