Abstract: Based on introducing the geology, casing program and well path, this paper analyzes the the challenges of hole trajectory in details, elaborates the trajectory control technology for underbalanced drilling of DP-19 slim-hole horizontal well with long horizontal section, sums up experience and recognitions in drilling of slim-hole horizontal wells with long horizontal section, providing valuable experience for enhancing the overall development performance of the low-permeability and low-pressure gasfield in Daniudi area. It also provides new and efficient techniques for trajectory control of long horizontal-section wells in anisotropic reservoir.