objective by measuring the VARIAN IX and 23 EX medical linear accelerator for 60 and 40 to dynamic multileaf collimator(DMLC)transmission between doses,leaf blade leakage of radiation dose,leaf position correction factor and inner and outer penumbra,analyze the reasons.Method using Kodak Xray film analyzer measurement Omat V VARIAN medical linear accelerator for 60 and 40 of the DMLC transmission between doses,leaf blade leakage radiation dose,leaf position correction factor and the inner and outer penumbra.Results VARIAN of different types of radiation leakage between the DMLC transmission factor,leaf blade factor correction factor,leaf position and the size of the inner and outer penumbra and DMLC type,size of the radiation energy accelerator are related.Conclusion with intensitymodulated radiation therapy and clinical application of rotating arc intensity modulated radiation therapy technology,the output of the accelerator machine hop count MU is very high,so the DMLC transmission,leakage and the location precision and the requirements of the inner and outer penumbra is higher and higher.Due to these parameters DMLC objective existence,it is necessary to do quantitative analysis in clinic,in optimizing radiotherapy plan should also according to the situation turned head use tungsten the door again to keep out important endanger organs and normal tissue,minimize the effects of these parameters on the treatment plan,in order to reduce the radiation risk.