Abstract: The coarse radial collimator which can reduce the background of neutron spectrometer plays an important role in the construction of China Spallation Neutron Source. The aluminum alloy 7A09 was chosen as the vacuum sealing material for coarse radial collimator. The different structures of the aluminum alloy window were designed by considering the requirement of neutron transmission and mechanical properties and the geometric constraints of the neutron flight path. The finite element simulation and analytical calculation were used to evaluate these structures and select a suitable sealing window structure eventually. The same methods were applied to the design of the collimator chamber and the design was got finally.