Abstract: The experimental technique of split Hopkinson pressure bar is an effective method to carry out an experiment in study of the dynamic behavior of materials. But some problems such as non-uniform dynamic stress in a specimen and non-constant strain rate during the experiment may arise if the technique isnt modified. Polyurethane foams have been widely used in civilian and military areas. It is more important to study their mechanical behavior, especially, dynamic behavior. The dynamic behaviors of a polyurethane foam under the conditions of uniform stress in the specimen and constant strain rate were detained experimentally with modified spilt Hopkinson pressure bar technique.