Abstract: Combined with the construction survey practice of steel-pylon in the third Yangtse River bridge of Nanjing, though the experiment of one-way trigonometric leveling astronomical refraction above the river at night simulating the on-the-spot environment, the changing regulanity of astronomical refraction quotiety was analyzed, and the ways of reducing the effct that astronomical refraction made on the precision of the bigonometic leveling were introduced. The, essay aimed at guiding the assembly of the steel-pylon at night. Tbe conclusions are practical to enhance the precision of bigohometric leveling.