Abstract: To address the problem that crossbeams of large vibrating screens are prone to fatigue fracture at the junction between the crossbeam seat plate and steel tube, and to investigate the influence of the seat plate structure on the stress and deformation of the crossbeam, force analysis of the vibrating screen was conducted. Combined with theoretical formulas of exciting force and the differential equation of the deflection curve, theoretical calculations of crossbeam bending deformation were performed. By means of finite element simulation, a comparative analysis was carried out on the influence of rivet bolt pretightening force and seat plate structural forms on the mechanical properties of crossbeams. The results indicate that: the maximum equivalent load on a single seat plate during upward acceleration of the screen body is 4886 N; the theoretically calculated maximum deflection of the crossbeam is 0.1693 mm, while the maximum deformation from simulation without pretightening force is 0.1757 mm, with a deviation of 3.8% between the two; rivet bolt pretightening force only causes local stress concentration around bolt holes, with a mean deformation deviation of sampling elements of merely −0.50% and an overall stress deviation not exceeding 10%; indicating that the pre-tightening force has a negligible effect on the overall deformation and overall stress distribution of the crossbeam; the three-in-one seat plate reduces crossbeam deformation by 10.70% and stress by 39.69%, whereas the hyperbolic seat plate reduces deformation by 2.03% and stress by 3.77%; both can improve the force-deformation behavior of crossbeams, while other seat plate structures slightly degrade mechanical indicators, with parameter deviations below 6%; the three-in-one seat plate offers the optimal mechanical optimization effect but involves higher processing and operating costs; considering comprehensive mechanical performance and economic cost, the hyperbolic seat plate is more applicable to industrial sites. This study can provide a theoretical basis for lightweight and high-reliability structural optimization design of seat plates for large vibrating screen crossbeams.