Abstarct: In the Common Steel structures, beam to column connections are usually designed supposing completely rigid or ideal pinned, but most of the real beams to column connections have the same behavior of semi-rigid connections. Semi- rigid connections are more interested to the researchers and a lot of researches have been done and continued. In this thesis at first, for modeling and analysis of web angles connections, top and seat angle, with ansys software. Each connection macros with user guide proposed dimensions for beams profiles runs in software. Using connection rotation angular majorment loaded moment, drown diagrams of each connections and elastic stiffness and plastic stiffness of each connections with different distance are obtained. Finally, a two story building with aspect connection stiffness and approximately with out these are analyzed and designed. Using of connection stiffness in structure design cause to decrease in beams profile. Consequently structure design reliability has bean increase. Therefore pay attention connection stiffness economize project planning.