The ?215.9mm four-cone coring bit is a cone coring bit designed and produced under the project of "Deep Sea Drilling Technology And Engineering Support"， and is mainly used for high-efficiency and long-run coring in hard rock and complex strata. By reasonably arranging the cone angle and distribution， and optimizing the coring structure， core recovery can be effectively improved to ensure the drilling rate and reliability of the bit in hard rock. Land test and marine test had been conducted for continuous optimization and improvement of the bit； and experimental geothermal exploration coring was carried out for the first time in Qingshuihe county， Hohhot city， Inner Mongolia autonomous Region. The whole coring section is granite of high abrasiveness and high hardness， and difficult to core. With the combination of the ?215.9mm cone coring bit with conventional coring tools， drilling speed reached 1.2m/h with core recovery of 70%~90%. It has good application value and can provide technical support for marine drilling hard rock coring.