The article introduces the results of indoor mud test and drilling mud test at Nanhai oil field using the sepiolite originated from Hunan Province. The analysis and the test show that the primary components of the clay are sepiolite, quartz, talc and a spot of calcite, and the particle size of the clay is influential to the mud productivity. The clay can be effectively dispersed in NaCl or Na 2CO 3 solution and build up stable viscosity, but it demands stronger shearing force while creating mud. The mud test at Nanhai oilfield had basically achieved the expectant purpose.