According to the facts of researches on disassembly sequence, the mathematical model of connected element hierarchy network graph and a method to generate disassembly sequence in the whole disassembly using connected element hierarchy network graph are proposed. The method can express disassembly model easily when the number of parts is too much or the relations among the parts are too complicated, which can provide theory basis for the products creating the automatic disassembly sequence and reduce the difficulty of disassembly process effectively. At last, a case study refer to screw pump is given to show that the method was applicable, effective and applied.