The utility model provides a cooling system of an improved three-roller planetary rolling mill, which comprises water spray rings and water spray cooling systems. Two water spray rings are arranged on a sealing shield, one water spray ring is arranged at the front end of the sealing shield, the other water spray ring is arranged near the front end of the sealing shield, and two water spray cooling systems are arranged at the back of a door plate of the sealing shield. By adopting the above technical scheme, the cooling system has the following beneficial effects: (1) one water spray ring is additionally arranged at the front end of the sealing shield, a roller and a rolling pipe are cooled at the same time, the cooling speed and degree are improved, and the uniform and complete degree of cooling are also improved, so as to lead the rolling pipe to be quickly cooled to the proper temperature range, thereby ensuring the quality of the rolling pipe; (2) as one water spray cooling system is additionally arranged at the back of the door plate of the sealing shield, the oxidizing degree of the rolling pipe is greatly lowered by dual cooling, thereby avoiding impact on products due to deficient cooling.