The invention relates to a three-phase four-wire low-voltage synchronous attenuation device which comprises a three-phase four-wire input coupling device and a three-phase four-wire output coupling device. The three-phase four-wire input coupling device comprises four ways which are 1 way, 2 way, 3 way and 4 way, the three-phase four-wire output coupling device comprises four ways which are 1 way, 2 way, 3 way and 4 way, and each way is provided with an input end and an output end; wherein the input end of the 4 way of the input coupling device is respectively connected with A phase, B phase,C phase and N phase of a three-phase four-wire system, the output end of the 4 way of the output coupling device is respectively connected with U phase, V phase, W phase and N phase of the another three-phase four-wire system, four attenuation devices are connected in series between the three-phase four-wire input coupling device and the three-phase four-wire output coupling device, each attenuation device is connected with a control device in a corresponding way, and each control device is connected with an interface device in the corresponding way. The invention has the advantages that a wave carrier test can be accurately carried out on communication products, and wide range and time-varying attenuation of a low-voltage power line is efficiently reflected.