Capacity based design of vertical boundary elements with regard to resisting expected yield strength of the web plate could be led to large column size. This key problem leads to a lack of widespread implementation of steel shear walls. This research project aims to investigate the formation of tension field in steel shear wall with partial length connection of web plate to vertical boundary element which in this type of steel shear walls, reducing the length of the connection leads to a reduction in the flexure and stiffness demand on the vertical boundary elements. For this purpose, the finite element modeling methodology was initially established and validated based on a laboratory test. Nine FE models were developed based on the verified specimens, and various not connected infill plate values. Finally, based on assumptions confirmed by numerical modeling and complementary experimental investigation, two governing equations have been developed for this type of steel shear wall, including panel shear strength, tension field inclination angle in the web plate in case, not connected length ratio is less than 30%.