The application relates to a structure of a watch strap and a watchcase which are fixed by a pressing structure engaging with an elastic pin. The watchcase is provided with a connection head, the connection head is provided with an elastic pin fixing hole adjacent to an end portion of the connection head and for disposing an elastic pin structure. An end portion of the watch strap is provided with the pressing structure and a connection head receiving recess. An end portion of the elastic pin structure in the elastic pin fixing hole is inserted into an elastic pin engaging hole defined in the watch strap by spring elasticity, an end portion of the pressing structure abuts against the end portion of the elastic pin structure in the elastic pin engaging hole. The structure is simple and practical.