A memory prototype of variation function based on COMPOSITE design pattern is proposed, through which a uniform visiting interface is implemented and greatly improves the maintainability and expansibility of indispensable code in whole project. Furthermore serialization of variation function and dynamically loading from storage is implemented with XML. Serialization of variation function with XML not only can store away model's information, but can reveal the inner structure of model, and provide basis of evaluation, analysis, contrast and selection of models, as well as repetition use of model under analogical geological environment.