Top Drive System is one great technological revolution for rig to replace Kelly and rotary table. Top Drive System can drill with triples instead of singles to reduce two-thirds volume of work of makeup and breakout, which greatly increases drilling speed. The advantages of TDS is if there’s block up or struck in tripping, you can rotate the drill string while circulating mud flow so it can reduce  drilling  accidents.  Top Drive System can increase the level of mechanization of operation together with the wellhead system which can reduce the worker's labor intensity and the amount of operators. Especially in the directional well and cluster well, TDS is an integrative system that consists of mechanical manufacturing, hydraulic controlling, electric engineering and many other technologies, and the reliability is the key criterium to inspect performance and manufacturing level of top drive drilling system.