The invention provides a dual wheel slot milling machine, comprising a guide frame, a sealing box body, a driving device and at least one milling wheel which is arranged on the lower part of the sealing box body and provided with a plurality of milling heads along the periphery of the milling wheel and can positively or negatively milling-dig soil layer and rock layer, wherein the driving device comprises a hydraulic motor with low rotary speed and big torque arranged in the sealing box body by the oil immersion lubrication sealing, and a variable speed transmission mechanism consisting of a small chain wheel arranged on an output shaft of the hydraulic motor, a big chain wheel used to drive the milling wheel to turn and a chain used to connect the small chain wheel and the big chain wheel. Due to the adoption of the structure of the driving device with the combination of the hydraulic motor with low rotary speed and big torque and the chain transmission, the slot milling machine is safe and highly efficient, and can perfectly construct the continuous wall with flattening, same thickness and big width, and the work efficiency, rotating speed and torque of the slot milling machine are almost the same as the imported equipment; moreover, the slot milling machine has the advantages of simple and reliable structure, low manufacturing cost, convenient assembly, disassembly and maintenance, low maintenance cost, energy conservation, environmental protection and easy popularization.