Abstract: In order to carry out technical study of coring drilling in large horizontal sections of horizontal wells, field experiments are conducted in the horizontal section of the Xing 6-1-Ping 35 well. In view of the coring characteristics and formation lithology, strong extended external gauge is designed for the PDC coring bits. Big-pitch cutting teeth are utilized. As a result, the coring bit works smoothly, and it has good chip removing effect and high stability. As a result, well deviation will be easily prevented. The drilling bit is resistant to wearing, because the gauge is made of natural diamond. So core blockage will not occur. Because the diameter is short in the cavity of the bit, the core will easily enter into the inner cylinder and the erosion of drilling fluids to the core will be decreased. Some key parts of the coring tool, i.e., the suspension linkage, the self-locking core-cutting device, the inner cylinder righting device, and the hydraulic ball-casting device are improved. And reasonable measures are developed. Combine with logging while drilling (LWD) techniques, double-stabilizer bottom hole assemblies are applied to tackle the difficulty in adjusting well path. The result is satisfactory. The core materials are ensured to be exact and complete. It provides effective methods for exploring and tapping the residual oil at the top of thick layers.