Because of concurrency and non-determinism, the inner-states of a running dist ributed program should be considered a part from the start and the end states, w hen the program is to be tested and the validated. According to specification ba sed testing, these inner-states will tranform into event sequences through the ports of the program, and the co-relations among these events, i.e. the set of event sequencing constraints should be provided by the program's specification. In this paper, the authors introduce the E-CSPE (extended-constraints on su cceeding and preceding events), a method to formalize these event constraints. T he E-CSPE includes three basic discription rules, which correspond to three dif ferent types of such event constraints. Based on the consistency with and covera ge of these event constraints by the event sequences produced by the program exe cution, the validity of the distributed implementation can be tested.