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Purpose:The purpose of this paper is to study the MLC leakage radiation between two rows of blades and between adjacent blades of 6 MV-X Flatting Filter Free(FFF)beam and Flatting Filter beam(FF)of the TureBeam accelerator.Methods:Combining with the TureBeam accelerator treatment head and MLC data provided by Varian,it is easy to study the treatment head,MLC and water phantom by using the codes BEAMnrc,DYNVMLC module and DOSXYZnrc,respectively.Under certain conditions of accelerator,Monte Carlo code calculate the leakage radiation when the blades were closed,then the data were verified by clinical experiments.Results:For FFF mode,the leakage radiation between two rows of radiating blades of Monte Carlo simulation and clinical experiments were found to be 22.7%and 24.5%,respectively.The differences of leakage radiation between each two adjacent blades were 0.4%~1.8%and 1.3%~1.8%,respectively.For FF mode,corresponding to the preceding data are 22.3%,24.1%,0.09%~1.37%and 1.13%~1.37%.By analyzing the simulation and measurement results of the off-axis dose curve,we can see the degree of deviation simulation and measurement results of less than 3%,and achieved a good agreement.Although theoretically FFF dose rate several times higher than the dose of FF,but the leak radiation amount is not corresponding multiple relationships.It is consistent with the data.Conclusion:Because of the 0.1 cm air gap between two rows of blades,the leakage radiation is more than 20%,when the blades were closed.Leakage radiation between two adjacent blades is about 0.09%~2.5%,and it is evident that the MLC meets the requirement of standard.On the basis of facts described above,the impact of 0.046 cm air gap can be ignored.For low tolerance dose organs at risk such as spinal cord and crystal,when using MLC shot blocked drain needs to fully consider the factors blade to the necessary protection.More considerations must be taken into account when using the MLC,thereby protecting the issue such as spinal cord and crystal that sensitive to dose radiation from damage.