Abstract: In view of the warping deformation of CRTS Ⅲ ballastless track slab of rail transit under the action of environmental factors, the temperature and vertical deformation taking place on actual operation line are observed and tested on site by sensors. The deformation patterns of the track slab under different environmental conditions and the influence of the track slab deformation on stability and comfort of train operation are studied. It is found that the temperature gradient is the main factor affecting the warpage of CRTS Ⅲ track slab. On a sunny Summer day, under combined action of solar radiation and ambient temperature, the deformation of track slab in daytime presents "upward convex", while it is "concave" at night, and the deformation amplitude of convex deformation is larger than that of concave deformation. Due to the reduction of solar radiation, the deformation of track slab is relatively small in rainy weather. The vertical deformation at the edge of track slab is larger than that of other parts in different environmental conditions. Through calculation, it is found that track slab deformation will affect irregularity of the rail, however the deformation value has little effect on stability and comfort of the train. Under extreme working conditions, stability and comfort indicators of the train are both excellent.Key wordsrail transit; ballastless track slab; temperature field; vertical deformation characteristics; environmental factors