Long span suspension bridges are subjected to daily, seasonal and yearly environmental thermal effects induced by solar radiation and ambient air temperature. The temperature loading effects of bridge towers of a long span cable suspension bridge are investigated based on field measurement data from temperature sensors and Global Positioning Systems. The recorded statistical data regarding the ambient/bridge temperature and the tower displacement responses are pre-processed in order to remove unreasonable and undesirable data and ensure the quality of analysis. The statistics of effective bridge temperature undergone by Tsing Ma Bridge are obtained for different time intervals. The mean displacement responses of the bridge towers in three directions are also analyzed to obtain their statistics. The observations demonstrate that the longitudinal thermal displacement of bridge towers is quite larger than those in lateral and vertical directions. The probability properties of thermal displacement of bridge towers are different to those of the commonly accepted Gauss distribution.