Recently, Z. Tang, and J. B. Dugan proposed a new algorithm (DEP-BDD) based on binary decision diagrams (BDD) for reliability analysis of phased-mission systems (PMS) with multimode failures. Although the variable ordering is very important from a practical point of view, it has not been treated directly. This paper develops four ordering heuristics for DEP-BDD based on two ordinary schemes, and evaluates these schemes & heuristics with hundreds of randomly generated fault trees having different sizes and structure properties. As a synthesis of the obtained performance results, we propose a heuristic selection strategy.