By using the wavelength encoding characteristic of fiber Bragg grating(FBG),a new kind of distributed FBG pressure sensor was introduced to achieve the train real time tracing.It combined FBGs of different wavelengths in series,and the space between them is same.When the wheel of the train is on the sensor probe,the center wavelength of the FBG will be shifted,the shifts time of each sensor should be the same,otherwise,it will mean that the disjoint is occurring.With computer monitor,the position,velocity,acceleration,and disjoint of the train can be given by analyzing the pressure acting time duration of each sensor.If there are more trains in the area,the distances of them can also be obtained.