Abstract: Serial investigation activities are conducted to the coiled tubing as failed,including visual analysis,dimension measurement,NDT and physiochemical property testing of the material.With consideration of its operation conditions and loading characteristics,the high instantaneous axial compressive load the coiled tubing bears is analyzed,and the bending-resistance of it at the wellhead is also carefully analyzed.Based on the overall analysis result,such a conclusion is made that it is the buckling of the coiled tubing that eventually leads to the said bending and breaking.Accordingly relevant preventative actions are proposed.