Mud cooling technology is one of the key technologies in gas hydrate drilling, the low-temperature mud will restrain the decomposition of gas hydrate in the process of drilling and drill lifting, which is favorable for discovering hydrate samples. The new gas hydrate mud cooling system consists of the ethylene glycol cooler, finned tube heat exchanger, temperature monitoring & recording and anti-frost device. Frequency conversion starting mode is used for the cooler, which can reduce the generator power and the cost of fuel consumption is significantly cut down. Convection heat transfer mode is applied for mud and ethylene glycol in the finned heat exchanger with large heat-exchange area and high efficiency. The temperature of these 4 key parts can be monitored and recorded by the temperature monitoring and recording device and the mud freezing and icing clogging in the heat exchanger can be prevented by the antifreeze device. By using the heat transfer theory and fluid mechanics, the theoretical calculation for heat convection process of mud and coolant is made, the results show that with heat-exchange area of 10.58m2 and pipe pressure loss of 0.34MPa, the cooling requirements can be satisfied.