Sets up Feiyunjiang bridge spatial model through the current finite MIDASCIVIL program, analyzes the main beam generating the coupling effect of bending and torsion in construction phase under the factors of constant load, shrinkage and creep, prestressing and temperature effects, meanwhile compares the various factors constributed to the main beam torque. The results show that in terms of space curved beam, tensioned prestress has a greater torque effect and the torsional stability of curved girder bridges is mainly reflected in the curved beam deformation and the reaction force on bearings，so it needs to set a reasonable form of support to ensure the torsional stability of the main beam.