Japan National Oil corporation (JNOC) has been in possession of an advanced Drilling-Test-System (DTS). This DTS can be used for full-scale indoor experiments and a series of tests on the rocks of Mudstone, Volcanic tuffs and Sandstone have been conducted by using it. The bit types used for those tests included PDC bit, Insert-tricone bit and Surface set Diamond bit. Bit performance is evaluated based on the values of the Rate of Penetration (ROP) and the impact on ROP of individual drilling variables. As a result, it is found that in comparison, the employed PDC bit appeared to be the most suitable bit for drilling on the rocks used for the tests. Meanwhile, tests using Water as drilling fluid were conducted and the results indicated that ROP and drillability could be significantly enhanced by improving the cleanness of bit and in-situ of bit. An embryonic model for PDC bit has been developed and verified to a certain extent. Further tests and analyses are still ongoing and it is expectable that, the results from the DTS test will significantly benefit to practical drilling optimization including bit selection, optimizing drilling and hydraulic parameters and diagnosing drilling problems.