This paper describes a site test on the deformation of loaded track by white light speckle method. The results obtained from double-exposured speckle patterns by pointwise method show that the resultant displacement at every point within the test section along the loaded track is not vertically downward as some people usually consider it to be. Each displacement has a horizontal component opposite to the direction of motion of the locomotive. The vertical components are different in magnitude and direction.In front of the pressed point under the test wheel of the locomotive there exists a certain point such that the vertical components at places behind this point are downward and at places in front of this point are upward. This particular point is an inflexion point. The part of loaded track behind this inflexion point sinks downward while the part in front of this point bends upward. This Phenomenon shows that the running locomotive creates an "elastic-wave" along the track. The maximum displacement of the loaded track is about 5 - 7 mm,and the relative error is within the limit of 1-5 % .