The invention discloses an upper disk and lower disk knitting mechanism for a double-sided automatic underwear machine. The upper disk and lower disk knitting mechanism comprises a needle dial seat, a cutting disk base, a large disk gear, a needle selector, a lower section needle cylinder, a saddle bottom ring and an upper section needle cylinder, wherein a needle dial is connected to the needle dial seat, a plurality of upper needles with high pins and low pins are connected to the needle dial, a cutting disk is connected to the cutting disk base, the right end of the cutting disk is connected with a yarn nozzle, the open latch end of the yarn nozzle is connected with needle latches of the upper needles with the high pins and the low pins, an air cylinder needle selecting device is connected to the cutting disk, the lower section needle cylinder is connected to the large disk gear, the needle selector is connected to the large disk gear, a pattern bit is connected to the lower section needle cylinder, the needle selector is connected with the pattern bit, the upper needle cylinder is connected to the lower section needle cylinder, a return triangle port is connected to the saddle bottom ring, the return triangle part is connected with the pattern pit, and an automatic needle walking triangular mechanism is connected to the saddle bottom ring. The upper disk and lower disk knitting mechanism has the advantages of being simple in structure, convenient to operate, automatic in needle selection and needle walking and practical.