Abstarct: BNCT or the Boron Neutron Capture Therapy is an effective method for the removal of some tumors. According to this method the tumor marked by the 10 boron, then the marked tumour bombarded by neutrons in appropriate intensity and energy. for boron neutron capture therapy we need a suitable neutron source. The neutron source must be able to meet our requirements, the different sources used for this, these sources have advantages and disadvantages. In this thesis, the use of plasma focus devices have been investigated as a neutron source, the survey carried out by the Monte Carlo simulation method. The output neutron beam from this source should have appropriate intensity and energy for using in BNCT. in order to optimizing the neutron flow it is nesessary to pass it from a beam shaping assembly befor it reach the patients body. In this study it has been tried to optimize the neutron beam by using materials with different thicknesses. The MCNPX6 is the computational code which is used in this thesis. our study has been done successfully the simulations results are mentioned at the end of the thesis.