Abstract: Firstly, according to the definitions in the ISO 9646 about the protocol conformance testing, some basic concepts of protocol conformance testing are presented. Secondly, the basic theory, definition, and properties of the labelled transition system （LTS） are given. By using the theory LTS, the test suite, test case and test generation are defined. Thirdly, the implementation relation which plays a important role in test generation is described. Finally, after giving the definition of the input/output system implementation relation, the implementation relation ioco is introduced, in which the input/output system and Δ transformation are used, and a test automation algorithm is given.