The utility model relates to a pressure-withstanding combined oil tank with multi-column plastic pipes, 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 urea reducer pressure-withstanding pipe bodies, 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; the urea reducer pressure-withstanding pipe bodies are hot-melted into one column by a welding coupling pipe, an upper pipe plug and a lower pipe plug, and are connected into a whole by welding zone joints; and the number of the urea reducer pressure-withstanding pipe bodies is 4 to 6. On the basis of a traditional automobile oil tank, the multi-column plastic pipes are combined to serve as the urea reducer pressure-withstanding pipe bodies and a urea reducer dose control box, so that one oil tank body has three functions, thereby realizing compact design, being beneficial for the design of beautiful appearance of a vehicle, reducing installation of connecting pieces, simplifying vehicle configurations and reducing the weight; therefore, 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.