Abstract: The progress of nuclear plant construction greatly intensify the market demand for indigenous digital instrument control system for nuclear power plants. However, it is hard to find the qualified suppliers who can provide numerous nuclear grade facilities for safety functions. We can only adopt non-nuclear grade facilities usually applicable to common industry standards from non-nuclear grade facilities suppliers, namely commercial grade items, which quality should be controlled and guaranteed as required by laws and regulations. With reference to current international experiences, we found that the Commercial Grade Dedication (CGD) has been proven to be a successful way. Basing on the designation and supplement of DCS for the generators No. 5 and No. 6in Tianwan Nuclear Power Plant, we studied related national and international standard and CGD methods and found a set of CGD system and methods suitable for NPPs in China. They have been proven to be successful in Tianwan Nuclear Power Plant, and should be a valuable reference for CGD for nuclear field in China, or even in the world.