In the paper, finite element models are established by using numerical methods to study the mechanical behavior of these kinds of connections. By discussing the range of design parameter of reduced beam section connection and widened beam section connection, stress distribution of connections and the influence of design parameter on bearing capacity at elastic stage and plastic stage are studied. The FEM models of these two kinds of connections behaved good ductility behavior. The purpose of moving plastic hinge outward from the beam and column interface is realized. Stress concentration near welds at the end of beam is reduced significantly. The bearing capacity of widened beam section connection increase obviously due to expanding the local area of beam flanges at the end of beam, but that of reduced beam section connection decrease due to trimming beam flanges. After studies, the range of design parameter of reduced beam section connection and widened beam section connection are given in the paper, and comparing with FEMA-350  of American. The suggestion parameters would be useful for seismic design of steel frames.