Embodiments of the present invention provide an encoding/decoding method, apparatus, and system, and relate to the communications field. The present invention may improve decoding performance and improve accuracy of a survivor path. The method includes: encoding information bits according to a first-level encoding method to obtain a first-level encoded code word; obtaining a sorting value of each check bit of the first-level encoded code word, and adjusting each check bit to a corresponding position according to the sorting value of each check bit, where the sorting value refers to a value of S when the check bit is related to first S information bits of the information bits in the first-level encoded code word, and S is a non-zero integer; and performing, according to a second-level encoding method, second-level encoding on the first-level encoded code word after positions of the check bits are adjusted, thereby obtaining a second-level encoded code word. The present invention is applicable to various communication systems.