In order to analyze the influence of web parameters on the torsional performance of flat multi-chamber box girder with partial load, Taking the main beam of the Linhai Bridge in Linhai City as the engineering background, the finite element model of flat multi-chamber box girder with different section forms was established using ANSYS to study the vertical displacement and torsional distortion angle of flat multi-chamber box girder with different mid-web spacing and mid-web thickness under partial load. The influence of different section forms on the torsional performance of the box girder was also evaluated. The results show that, the overall torsion of section is mainly caused by box girder with transverse diaphragm under partial load. The torsional performance of box girder is impacted significantly by the web parameters. The torsional stiffness of the box girder can be improved by the reasonable adjustment of the spacing and thickness of the web. When the middle web spacing d is10.0m, the torsion stiffness of the box girder section is increased by 15.7% compared with that of 0.0m. When the middle web thickness t3 is 0.0m, the torsion stiffness of the box girder section is 38.2% higher than that of 0.60m. Furthermore, the increase of the number of web can improve the bending performance of the box girder, improving the connection between the top and bottom of the box girder. and the overall stability of the box girder is improved. This conclusion can provide theoretical reference for similar box girder section design.