According to the revised Cailikefu′s rolling shear force formula, motion path equation of spatial seven-bar path was built, and a mechanical model, with the new structural feature of negative offset, was thus successfully established for 2 800 mm heavy shear of some iron and steel company. Shear and bar forces of steel plate, before and after the adoption of negative offset structure, were analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. It was found that the back-wall push force keeps large even at the time that the maximum rolling shear was obtained; meanwhile, back-wall push force is the most approximate to side forces when 60-100 mm of offset was adopted. Both theoretical results and on-site shear quality show that the negative offset plays an important role in ensuring the stability of pure rolling shear and keeping blade clearance constant. According to the revised Cailikefu’s rolling shear force formula, motion path equation of spatial seven-bar path was built, and a mechanical model, with the new structural feature of negative offset, was thus established successfully for 2 800 mm heavy shear of some iron and steel company. Shear and bar forces of steel plate, before and after the adoption of adoption of negative offset structure, were analyzed as as as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. It was found that the back-wall push force was the most approximate to side forces when 60-80 mm of offset was adopted. Both theoretical results and on-site shear quality show that the negative offset plays an important role in ensuring the stability of pure rolling shear and keeping blade clearance constant.