Welding technology is one of the core technology of equipment manufacturing.Belt transmission is an important device of reducing mechanism of cantilever welding positioner to transmit motion and power.Using MATLAB,multi-objective optimization for belt transmission device was realized. The number of bands was reduced in meeting the conditions of carrying capacity.The diameters of the pulley and center distance were reduced.So the transmission structure was more compact.Using RecurDyn software,simulation analysis for belt transmission was carried out.The virtual prototype model of the belts was established.The relevant kinematic curve was obtained.It provides theoretical basis for design and calculation of belt transmission.