Where do I get full documentations besides the user guide and tutorial?Becuase I want to know more on the computational structure, capabilities to various types of applications and the modeling environment.

The User Guide and Tutorial are the only official documentation, but you can read the publications on the website ( http://www.weap21.org/publications ), which detail many case studies. You can find some technical details of WEAP in the 2005 Water International paper ("WEAP21--A Demand-, Priority-, and Preference-Driven Water Planning Model: Part 1, Model Characteristics").