Research conclusions :(1) Based on adjacent chord azimuth changes，the method of approximate segmentation can handle different curve radius measured data, and the result meets the requirement of fitting and iterating calculation.(2)By contrast of the segmentation results between measured data and design data，the method of plane accurate segmentation can achieve high segmentation accuracy.(3)By contrast of the segmentation results between measured data and design data, the method of vertical linear accurate segmentation is correct and the high accuracy can be achieved. (4) The research achievement can be applied in measured linear calculation，and has the reference value for linear adjustment in existing railway.