The utility model relates to a small and medium-sized drilling machine drilling fluid closed circulation system. The problem that drilling fluid landing circulation cannot meet the environmental protection requirement in the existing drilling process is mainly solved. The device is characterized in that the drilling fluid tank A is connected with a stirrer and two vertical pumps, two vibrating screens (2) are arranged on the drilling fluid tank A, and the drilling fluid tank A (1) is connected with a drilling fluid tank B (13) through two vertical pumps (5); the drilling fluid tank B is isolated into four bins; the drilling fluid tank B is connected with two vertical pumps (5) and a stirrer (4), a desanding and desilting device (6) is further arranged on the upper portion of the drilling fluid tank B, outlet lines of the two vertical pumps B are connected with the desanding and desilting device, and the lower portions of the two vertical pumps B and the desanding and desilting device correspond to a desanding bin (15). According to the small and medium-sized drilling machine drilling fluid closed circulation system, the drilling fluid circulation technological process is optimized,the drilling fluid circulation system is optimized, and the requirements for drilling production environmental protection and the technology are met.