The invention discloses a device and method for testing a common mode rejection ratio of a polarization multiplexing balance coherent receiver. The method comprises the steps that a first tunable laser device, a first polarization controller, a first variable optical attenuator and a first 1*3 optical switch are connected; a second tunable laser device, a second polarization controller, a second variable optical attenuator and a second 1*3 optical switch are connected; a first output port of the first 1*3 optical switch and a first output port of the second 1*3 optical switch are connected with two optical power collecting ports of a data collection and control unit respectively; a third output port of the first 1*3 optical switch and a third output port of the second 1*3 optical switch are connected with two light splitting ports of an optical coupler respectively; communication ports of the data collection and control unit are connected with communication ports of all the devices respectively. The device has the advantages that the structure is simple, operation is convenient, and data are processed easily.