In order to investigate the influence of temperature gradient on the construction of wide extradosed cable-stayed bridges in the large cantilever construction stage at high temperatures，the solar radiation and thermal boundary conditions of wide equal-height box girder were theoretically calculated，and the thermal analysis finite element model of the wide equal-height box girder was established by Abaqus.The cross-section temperature of the box girder was measured by intelligent string sensors and an infrared thermometer.The temperature gradient and its distribution of wide equal-height box girder from sunrise to sunset on a certain day in summer were calculated.The finite element model of the construction stage was established by Midas Civil，and the influence of positive temperature gradient on the main beam alignment and stress under control conditions of a large cantilever was analyzed.The results show that the results of the thermal analysis finite element model are in good agreement with the measured temperature results.The temperature gradient effect at the side and middle web of the wide equal-height box girder is the most significant.During the noon period at high temperatures，the vertical temperature gradient and the range of action at the top of the side and middle web of the wide equal-height box girder are higher than the specified value of the General Specifications for Design of Highway Bridges and Culverts （JTG D 60—2015）.The positive temperature gradient causes the main beam to deflect，and as the cantilever increases，the deflection effect of the main beam is more significant.Compared with no temperature gradient，the deflection of the cantilever end of the main beam increases by 36.08 mm after the maximum cantilever segment pouring，and the deflection of the cantilever end of the tail-cable tensioning main beam increases by 40.23 mm.The positive temperature gradient makes the compressive stress on the roof of the main beam increase significantly.