Abstract: MPD is a new technology that to resolve the drilling problem of narrow mud weight window, the aim is to precisely control the annulus pressure profile, to achieve a constant bottom-hole pressure. This article describes the development of the PCDS-I Auto-controlled pressure drilling system, equipped with sophisticated features, field tests and application. The overall stable operation, without failure, has withstood the test of site conditions, to achieve a constant well base pressure control, and micro-flow control, into the process system back pressure control accuracy 0.2 MPa, then a single root, from the drilling process control precision of the system back pressure 0.5 MPa.