The invention discloses a phase shifting method applied to a power line communication system, comprising the steps of dividing a signal to be transmitted into signal segments of a first preset value group, wherein the number of sub-carriers in each signal segment is not greater than a second preset value; traversing and calculating a peak-to-average power ratio (papr) of all the phase offset combination segments of the sub-carriers in each group of signal segments; combining the phase offset combination segment with the lowest papr in each group of signal segments into a complete phase offsetcombination according to the original order of the sub-carriers, and combining the phase offset combination segment with the lowest papr in each group of signal segments into a complete phase offset combination; performing phase shift on a plurality of sub-carriers in a signal to be transmitted according to the phase shifting combination. The invention can smoothly complete a large number of PAPRcalculations, reduces the PAPR of signals to be transmitted, and reduces the cost of the power line communication system and the bit error rate. The invention also discloses a power line communicationsystem, a phase shifting device and a device thereof, which have the same beneficial effects as the above phase shifting method.