The invention discloses a truck fuel tank with an auxiliary fuel tank function. The truck fuel tank with the auxiliary fuel tank function comprises a fuel tank body. The fuel tank body comprises a main oil tank and an auxiliary oil tank arranged in the main oil tank. The main oil tank is provided with a fueling nozzle. The fueling nozzle comprises a fueling port connecting with the main oil tank and a fueling inner bushing extending into the auxiliary oil tank. The bottom of the fueling inner bushing is provided with an opening connecting with the auxiliary oil tank. A rotatable oil and gas sealing piece is installed on the opening. The rotatable oil and gas sealing piece is located inside the auxiliary oil tank. The side of the auxiliary oil tank is provided with a plurality of oil spillholes connecting with the inside of the main oil tank. The truck fuel tank with the auxiliary fuel tank function has a simple structure and is convenient to use, the fuel stored in the auxiliary fueltank can be used when the fuel in the main fuel tank is used up, thus fuel replenishment is realized, the trouble of running out of fuel when the truck runs on a highway or an open section with no gasstation nearby is effectively reduced, and convenience is brought for novice drivers and drivers who forget to refuel in negligence.