Abstract: A new system of phased array radar is assembled by digital array units(DAUs),of which the antenna size is determined by the number and construction of DAUs.To obtain low sidelobe level,tolerance analysis is applied to the antenna array composed by DAUs and the relationship between DAU features and surface planeness error are studied.Futhermore,by accurately modeling and orientation tolerance analysis,an credible surface planeness analysis software of the antenna array after compared to the actual array data is developed.