The embodiment of the invention discloses a coding method, a coding device, a decoding method, a decoding device, a coding system and a decoding system. The coding method comprises the following steps that: a coder acquires data to be coded, wherein the data to be coded is at least one largest coding unit (LCU); the coder determines a quantization depth parameter of the LCU according to a code rate control algorithm, and writes the quantization depth parameter into the data to be coded; the coder determines a quantization parameter (QP) of each CU according to a minimum image block dimension and the dimension of each CU in the LCU; the coder calculates a QP difference of each CU according to the QP and a QP predicted value of the CU; for each CU consistent with a preset condition, the coder carries the QP difference of the CU into the CU; and the coder codes the quantization depth parameter, the QP difference of the CU consistent with the preset condition and each CU to obtain a code stream. The embodiment of the invention also provides the decoding method, the coding device and the decoding device. By the embodiment of the invention, code rate control accuracy and compression efficiency can be effectively improved.