The invention provides an R shaft structure of a silicon chip transmission robot. The R shaft structure of a silicon chip transmission robot has the advantages of high revolving accuracy, high connection rigidity, simple structure and space saving and is particularly suitable for narrow space structures. The R shaft structure comprises an R shaft large arm shell mechanism (1), an R shaft large arm synchronous belt and pre-tightening mechanism (2), a coaxial seal mechanism (3), a synchronous small belt wheel rotating mechanism (4), a synchronous big belt wheel rotating mechanism (5), a cross bearing (6), a transmission shaft mechanism (7), an R shaft forearm synchronous belt and pre-tightening mechanism (8), an R shaft forearm shell mechanism (9) and the like. The structure provided by the invention has the characteristics that the mechanism in the traditional structure, which consists of one series of parts, such as one pair of angular contact ball bearings, bearing spacer bushings, bearing glands, bearing lock nuts and the like, is replaced by one cross bearing (6), so that the length of the transmission shaft is effectively shortened, the height space of the large arm and the forearm of the R shaft is reduced, and one series of functions are accordingly improved.