The present invention relates to a cross-band power line frequency recognition method based on a fine frequency granularity, comprising: establishing a power line communication (PLC) system model; dividing an operating frequency into a low frequency, an intermediate frequency and a high frequency, and acquiring, according to fine frequency granularity features, a low-frequency fine frequency granularity subband, an intermediate-frequency fine frequency granularity subband and a high-frequency fine frequency granularity subband; measuring power line channel noise of a master station and a slave station; calculating power line channel attenuation of an uplink and a downlink; calculating a link quality indicator (LQI) of the uplink and the downlink; and setting an LQI threshold, acquiring an available fine frequency granularity subband, and performing spectrum aggregation on the available fine frequency granularity subband. The present invention can perform recognition of a fine frequency granularity respectively on different bands of low frequency, intermediate frequency and high frequency by cross-band expansion of PLC frequency resources, so that the PLC can adequately search for a communication frequency and establish a stable communication link under extremely adverse channel conditions.