Abstract: The Ordered Binary Decision Diagram （OBDD） is used widely in digital design formal verification．However，the size of an OBDD is very sensitive to variable ordering．In this paper，a self-adaptive selecting algorithm proposed is based on a fast and effective measure for evaluating variable ordering，to select the “best” ordering among a group of orderings．The experimental results applied to ISCAS85 benchmark circuits demonstrate the practicability of our approach．