Abstract: This paper analyzes the friction and other forces exerted on the coiled tubing. To reduce largely measuring errors, the data from the horizontal well have been processed by means of the method of least squares; for the convenient of numerical calculation, the cubic spline function has been introduced, and thus the separated point data of the well became a C2 continuous curve. The frictional resistance model of 3-D curve locus has been established. After a series of deduction, a differential equation that can be solved by four orders Longe-Kutta method has been acquired. Thus,the sections’ forces,moments and stresses of coiled tubing are obtained.