The utility model relates to a pressure-withstanding combined oil tank with a two-column plastic pipe, which is characterized in that: one side of the combined oil tank is provided with a fuel oil tank body, the middle part is provided with an urea reducer pressure-withstanding pipe body, and the other side is provided with an electric control cabinet; one side of the electric control cabinet is provided with a buckling plate of a seaming end cover; an urea reducer tank cover is arranged on the urea reducer pressure-withstanding pipe body and is connected with a compressed air power input pipe and an urea reducer output pipe; a liquid level sensor is fixed on the urea reducer pressure-withstanding pipe body; the lower part of the urea reducer pressure-withstanding pipe body is provided with an urea reducer dispersing valve; a plastic pipe clamp is fixedly connected on the tank body; and a welding coupling pipe, an upper pipe plug and a lower pipe plug are hot-melted into one column connected with another column into a whole by a welding zone joint. Therefore, one oil tank body has three functions; compact design is realized, which is favorable for the design of beautiful appearance of a vehicle; in addition, installation of connecting pieces is reduced, vehicle configurations are simplified and the weight is reduced. The pressure-withstanding combined oil tank not only can meet the standard requirements of SCR (selective catalytic reduction) higher than national grade IV, but also can realize reduction of the system cost.