The invention relates to an oil way system with a cooler being arranged outside the ship board. The oil way system comprises an oil tank with an oil return port and an oil outlet port, an operation element communicating with an oil outlet pipe and the oil outlet port, the cooler communicating with the operation element through a first oil returning pipe, and a second oil return pipe communicating the cooler with the oil return port, wherein the cooler is detachably arranged on the outer side of the ship board and located behind a paddle wheel and is close to the paddle wheel; and when the ship is on the water, the cooler is located under the water surface. The cooler is close to the paddle wheel and is located outside the ship board, an oil way is cooled through large-flow clean water, return oil can achieve the optimal cooling effect, meanwhile, the cooler can be taken down from the ship board to be cleaned at any time, the structure is simple, operation is convenient, the cost is low, and the oil way system is quite suitable for small water surface cleaning vessels.