A wheel assembly for a universal wheel, comprising a welding shaft for a universal wheel, the welding shaft for a universal wheel comprising a big wheel welding shaft and a small wheel welding shaft, the big wheel welding shaft comprises a big wheel welding shaft body, a big wheel welding shaft retainer ring and a big wheel welding shaft fixing head, and the small wheel welding shaft comprises a small wheel welding shaft body, a small wheel welding shaft retainer ring and a small wheel welding shaft fixing head, the wheel assembly further comprising a wheel shaft fixing plate, a big wheel, a small wheel, the big wheel is connected to the big wheel welding shaft body of the big wheel welding shaft, and the small wheel is connected to the small wheel welding shaft body of the small wheel welding shaft, the big wheel is connected to the big wheel welding shaft body of the big wheel welding shaft, and the small wheel is connected to the small wheel welding shaft body of the small wheel welding shaft, characterized in that a big wheel shaft fixing hole and a small wheel shaft fixing hole are formed in a surface of the wheel shaft fixing plate and are close to a head of the wheel shaft fixing plate and are distributed in a lengthwise direction of the wheel shaft fixing plate; the big wheel welding shaft body, the big wheel welding shaft retainer ring and the big wheel welding shaft fixing head are sequentially assembled into a whole, and the small wheel welding shaft body, the small wheel welding shaft retainer ring and the small wheel welding shaft fixing head are sequentially assembled into a whole; a length of the big wheel welding shaft body is greater than that of the small wheel welding shaft body; the big wheel welding shaft retainer ring is in the shape of an incomplete circle; the small wheel welding shaft retainer ring is in the shape of an incomplete circle; the big wheel shaft fixing hole and the small wheel shaft fixing hole are distributed in a lengthwise direction of the wheel shaft fixing plate, a distance from the big wheel shaft fixing hole to the head of the wheel shaft fixing plate is greater than a distance from the small wheel shaft fixing hole to the head of the wheel shaft fixing plate; the big wheel welding shaft fixing head of the big wheel welding shaft is inserted into the big wheel shaft fixing hole from one surface of the wheel shaft fixing plate and is fixedly connected to the big wheel shaft fixing hole through welding, the small wheel welding shaft fixing head of the small wheel welding shaft is inserted into the small wheel shaft fixing hole small wheel shaft fixing hole from another surface of the wheel shaft fixing plate and is fixedly connected to the small wheel shaft fixing hole through welding. the big wheel welding shaft body, the big wheel welding shaft retainer ring and the big wheel welding shaft fixing head are sequentially assembled into a whole, and the small wheel welding shaft body, the small wheel welding shaft retainer ring and the small wheel welding shaft fixing head are sequentially assembled into a whole; a length of the big wheel welding shaft body is greater than that of the small wheel welding shaft body; the big wheel welding shaft retainer ring is in the shape of an incomplete circle; the small wheel welding shaft retainer ring is in the shape of an incomplete circle; the big wheel shaft fixing hole and the small wheel shaft fixing hole are distributed in a lengthwise direction of the wheel shaft fixing plate, a distance from the big wheel shaft fixing hole to the head of the wheel shaft fixing plate is greater than a distance from the small wheel shaft fixing hole to the head of the wheel shaft fixing plate; the big wheel welding shaft fixing head of the big wheel welding shaft is inserted into the big wheel shaft fixing hole from one surface of the wheel shaft fixing plate and is fixedly connected to the big wheel shaft fixing hole through welding, the small wheel welding shaft fixing head of the small wheel welding shaft is inserted into the small wheel shaft fixing hole small wheel shaft fixing hole from another surface of the wheel shaft fixing plate and is fixedly connected to the small wheel shaft fixing hole through welding.