<p>In the long-distance horizontal directional drilling engineering with the complex geological environment, the technology of rapid coring has been applied to obtain the geological information. However, it is hard to achieve the integrity and efficient transportation in the process of rapid coring. A rapidly growing field of water-based drilling fluids has been developed to resolve these problems from the view point of the drilling fluids. This work contributes to establish a structure-property relationship between the chemical modification of sepiolite and the water-based drilling fluids. The chemical structure of the chemical modification of sepiolite is characterized by FTIR and WAXD. TEM is employed to describe the microstructure of the sepiolites. The chemical modification of sepiolite is used to prepare the water-based drilling fluids WDF-01, WDF-02 and WDF-03. The comparative case WDF-00 is prepared on basis of the raw sepiolite. The basic properties of the water-based drilling fluids, such as rheological properties and API filtrate loss volume, are studied in the laboratory. Through chemical modification, the dispersion state of sepiolite in water is enhanced, which is helpful to produce better rheological properties for the water-based drilling fluids. Owing to the presence of lamellar structure in the raw sepiolite being improved by the chemical modification, the water-based drilling fluids on basis of the modified sepiolite possess good lubricity and low filter cake friction which are required by the horizontal directional drilling engineering. We expect that the study can provide significant reference for the realization of fast coring in the long-distance horizontal directional drilling.</p>