A method and system for serial data transmission are provided. The method includes steps of: bit-synchronously receiving N bit binary code data which is transmitted continuously and repeatedly by a transmitting end, wherein the N bit binary code data is N bit binary code data converted from original data by the transmitting end on the basis of a preset rule; performing cyclic left shift or right shift 0 to N−1 times on each of the received N bit binary code data, which results in a data set, and obtaining an extreme value in the data set; and decoding the extreme value, which results in the original data transmitted by the transmitting end. With the method and system, a start and an end flags are not needed to be added additionally during the serial data transmission, thus improving the efficiency of the serial data transmission.