Abstract: Platform horizontal wells are the main form to develop tight oil in Daqing Oilfield. The way placing wells on platform leads to 3D well sections in some horizontal well trajectories. During drilling process, compared with 2D horizontal wells, 3D horizontal wells have greater friction upon drill string, which limits the extension limit of horizontal wells. On the basis of the soft string theoretical model, by analyzing the contact form between the drill string and the borehole wall in the 3D well section, the model calculating shifting of the drill string was given, which was verified by integrating Landmark software simulation with actual drilling situation. The simulation results show that the contact area between the drill string and the borehole wall in the 3D well section is larger than that of the 2D well section, that the deviation angle is positively correlated with the friction upon drill string when adjusting orientation, and that the overall friction coefficient of 3D horizontal wells is above 0.4. During design process or drilling process, it is necessary to reduce the friction upon drilling string according to the friction generation law in the 3D well section, and some means may help, such as optimizing horizontal well trajectory and wellbore structure, reasonably allocating the position of the heavier drill pipe in drilling tool assembly, improving the lubricity of drilling fluid, and selecting friction reduction tools. Reducing the friction upon drilling string can effectively lengthen platform horizontal wells, which will ensure efficient development of tight oil platforms.