Abstract: The open loop field test of the new nitrogen circulation drilling system has been done for the first time to decrease nitrigen drilling cost and update drilling technology, that is, nitrogen is discharged after separating process, as a result the performance of separting and filtering equipment and its applicability of to drilling technology could be examined. In order to assure successful test, air tight test, regular drilling process test, and formation water production process test are designed. The result shows that the new technology is easy to handle and the whole system is credible. Particle size and content of the drilling cuttings in nitrogen after separation are all less than that of the local atmosphere, which is suitable to be injected into the compressor and booster again. This is helpful for the cyclic utilization of the costly nitrogen. Based on the analysis of problems during field test, some improved solutions are put forward. The new nitrogen circulation drilling system can be used widely after further improvement.