The temperature effect was of crucial importance to estimate structural state of existing PC cablestayed bridges. Taking Yonghe Bridge in Tianjin as a case, the influence of temperature effect, including temperature change of whole bridge, difference in temperature of cable and main girder, temperature Gradient in the transverse section of main girder, and temperature gradient in the transverse section of tower, was analyzed on geometry of bridge deck, inclined displacement at the top of tower and cable force. Based on observation data of Yonghe Bridge during the First and Second maintenance, effectiveness of temperature effect analysis based on the present bride code in China was verified. And then a modifying method of temperature effect in structural state estimation was proposed. It was shown that the temperature change of whole bridge and the difference in temperature of cable and main girder were the main factors to inclined displacement at the top of tower, and the difference in temperature of cable and main girder was the main factor to the deflection of main girder. Although a small error between measured and theoretical results caused by the rigidity deterioration of old bridge, the temperature effect analysis based on the present bride code in China could be feasible in structural state estimation of existing PC cablestayed bridges and provided reference for maintenance and construction control.