The internet is considered as the most extensive market in the world. To keep its gradual reputation, it must confront real problems that result from its distribution and from the diversity of the protocols used to insure communications. The Web service technology has diminished significantly the effects of distribution and heterogeneity, but there are several problems that weaken their performance (unavailability, load increase of use, high cost of CPU time...). Faced with this situation, we are forced to move in the direction of the substitution of web services. In this context, we propose an effective technique of substitution based on a new method of matching that allows detecting and expressing the matching between the web services pairwise by considering that each of them is ontology. Also, our method performs a discovery of the most similar web service to that to be replaced by using an efficient method of similarity measurement.