Mud cooling is a key technology of middle-high temperature geothermal drilling, deep oil & gas drilling, permafrost drilling and gas hydrate drilling operation. Proper temperature of circulation drilling mud is the guarantee for safe and fast drilling operation. According to the feature of cooling sources, drilling mud cooling technology would be divided into hightemperature cooling technology and low mud cooling technology. The paper respectively discussed high-temperature drilling mud cooling technology in the middle-high temperature geothermal drilling and the deep oil & gas drilling; and the low temperature drilling mud cooling technology in permafrost drilling operation and gas hydrate drilling operation. In view of the current situation of low temperature drilling mud cooling technology, a new type of drilling mud cooling system was developed.