The application and promotion of the SAW tag are unsatisfactory due to the inherent defects of the manufacturing technology and limitied capacity.From the perspective of practical production,the design scheme of medium capacity and largy capacity SAW tag based on the pulse position coding method is proposes,which can reduce costs besides increasing capacity.The largy capacity SAW tag is designed based on the correlation interditigal transducer(IDT) and permutations and combinations theory.At the same time, some ideas about the reader structure for this large capacity SAW tag are given.