A power calculation method including obtaining a first optical signal and a second optical signal; detecting first optical power of each waveband in the first optical signal and second optical power of each waveband in the second optical signal; calculating, based on the first optical power, a first optical power variation that is of each waveband of the first optical signal and that is used after the first optical signal is transmitted from a transmitting end to a receiving end, and calculating, based on the second optical power, a second optical power variation that is of each waveband of the second optical signal and that is used after the second optical signal is transmitted from the transmitting end to the receiving end; and determining a first compensation value and a second compensation value based on the first optical power variation and the second optical power variation.