The present application relates to multi-stage amplitude modulation-based methods, apparatuses, and systems for coding and decoding a visible light signal. The coding method includes the following steps: dividing to-be-transmitted information into multiple information units, where each information unit includes multiple bits; converting the multiple information units into multiple electrical signal units indicated by at least three levels, where an interval indicated by a first level in the at least three levels exists between adjacent electrical signal units, and each electrical signal unit uses a combination of other levels in the at least three levels to represent the multiple bits of a corresponding information unit; combining the electrical signal units to obtain a coded electrical signal; and transmitting the coded electrical signal in a visible light signal form.