Abstract: Abundant reserves of unconventional oil & gas resources occur in China. Exploring drilling and completion technology systems for the economic and efficient development is the key to speeding up the exploration and development process and scale up their production. This paper expounds the drilling and completion technology systems developed by Chinese researchers for unconventional oil & gas at less than 3 500 m depth. The key technologies in the systems involved wellbore trajectory design for three-dimensional cluster horizontal wells, design and operation of geology-engineering integration, rate of penetration (ROP) enhancement through drilling parameter optimization, managed temperature drilling of deep shale gas, geosteering, high-performance drilling fluid, and efficient cementing, etc. Nevertheless, it was noted that this systems still fell short in several ways. For example, optimal implementation of factory operation has yet to be achieved, the repeatability of horizontal well drilling with long horizontal sections was poor, the "one-trip drilling" technology and supporting equipment were not well established, and high-temperature and high-pressure (HTHP) resistant materials and supporting drilling tools were scant. Suggestions for further improvements were also put forward, such as accelerating the promotion of factory operation for large-platform cluster horizontal wells, continuously optimizing drilling technologies for horizontal wells with long horizontal sections, fulfilling the notion of geology-engineering integration, and conducting research & development (R & D) of HTHP resistant materials and developing supporting tools. These measures were expected to substantially boost the single well production and the recovery rate and thereby achieve efficient exploration and development of unconventional oil & gas.