Abstract: The principles and methods are introduced, which are used to encode parameters when applying the genetic algorithms in Ada structural testing. First , two main principles of encoding are introduced. Because Ada language could use dynamic data types in its parameter tables, the method used to handle them would be the most important problem when we want an automatic dynamic testing tool . Secondly , encoding methods used in both enumerative data types and dynamic data types are introduced. Parameters of enumerative data types have the same property. They can be encoded in the same way of integers. Encoding methods of the parameters of dynamic data types are emphasized.