Working Channel (CH) tuning methods, devices and system, an Optical Network Unit (ONU) and an Optical Line Terminal (OLT) are provided. In a working CH tuning method, at least one of the following information is provided for an OLT: a working CH corresponding to minimum power consumption or power consumption information corresponding to an ONU in different CHs. A tuning message which indicates an optimal working CH and is provided by the OLT according to the provided information is received from the OLT. A working CH is tuned to the optimal working CH indicated by the tuning message.