A coaxial structure of auxiliary wheels and a primary wheel includes a frame, an axle, a primary wheel and two auxiliary wheels. The frame is pivotally connected to the axle. Both the primary wheel and the auxiliary wheels are separately inserted with bearings or sleeves. The bearings or the sleeves are further inserted onto the axle. Both the primary and the auxiliary wheels wear tires made of different material to increase the contact area with the ground while the frame is inclined to take a turn to prevent from turning over.