Presently there exist several methods to evaluate the pollen viability including viability stain and in vitro germination, among which the in vitro germination method is thought to be more persuasive (Galleta, 1983). A fixed so-called “optimal” condition is usually used in the determination and comparison of pollen viability. Through our experiments, we found in pecan the rehydrationcondition was one of the keys to understand the durable abilityof pollen germination. That is to say, pecan pollen actually doesn’t lose their viability rapidly but move to a different state in first several days. If we continue using the initial experimental condition