In order to implement the automatic generation of binary decision diagram (BDD) for phased mission system reliability analysis, a universal approach for establishing BDD reliability model was proposed. A nested BDD data structure named BDD_Element was defined, and the approaches of BDD description and storage were given. Algorithms for transforming AND Gate, OR Gate and k/n Gate into BDD models were proposed. The BDD model for reliability analysis of phased mission system was constructed in 2 steps: based on the logic gate transforming algorithms, structure functions of the component logic relationship were transformed into phase BDD models; based on the BDD manipulation rules, phase BDD models were integrated together. By analyzing the reliability of satellite attitude adjustment mission, it shows that this approach can be effectually applied in the reliability analysis of phased mission system.