Abstract: In order to fully exploit the technical advantages of PDC bit in rock breaking, and to further improve its ROP in low permeability formation drilling, a two-stage and two-speed drilling tool was studied and designed. A numerical simulation method was used to establish the bottom hole petrophysical model during the two-stage and two-speed drilling, stress field distribution and rock breaking/speed-up mechanisms of two-stage and two-speed drilling were analyzed. The common structure of two-stage and two-speed drilling tool and its technical advantages were presented. Based on the research results and field site requirements, the two-stage two-speed drilling tools for ϕ215.9, ϕ241.3 and ϕ311.1 mm diameter borehole were optimally designed considering flow rate, output torque and rotary speed, drilling tool length, etc.. The tool was tested in 3 wells of Shengli Oilfield and it showed that the WOB, pumping pressure and tool performance are stable, and the ROP is 80.37% higher than that of the offset wells with normal tools. The designed two-stage and two-speed drilling tool presents a good comprehensive performance and can be used to improve ROP in low permeability formation drilling with good application prospective.