Abstract: The coiled tubing (CT) drilling technology is extensively employed in various operations of oil wells.The residual deformation of the CT caused by the winding on the reel has a magnificent effect on its extension length in horizontal wells. The friction curve fitting functions for various ratios of the diameter of the pipe to that of the tube and the residual deformation curve are obtained through similar experiments. The similarity of the model experiment and the actual coiled tubing operation is analyzed and the similarity constants are obtained, and then the friction between the coiled tubing and the casing wall is calculated. The final results show that the friction of a 2-inch CT with a residual deformation in the horizontal well is about 2.3 times of that of the CT without the residual deformation.