The invention discloses a multi-RT-PCR (Reverse Transcription-Polymerase Chain Reaction) method for synchronously detecting four porcine coronaviruses. The four porcine coronaviruses comprise RT-PCR primers of PHEV (Porcine Hemagglutinating Encephalomyelitis Virus), PEDV (Porcine Epidemic Diarrhea Virus), TGEV (Porcine Transmissible Gastroenteritis Virus) and PDCoV (Porcine Deltacoronavirus); a RT-PCR kit for synchronously detecting the four porcine coronaviruses comprises the RT-PCR primers for synchronously detecting the four porcine coronaviruses including the PHEV, the PEDV, the TGEV and the PDCoV; the invention provides an RT-PCR system for synchronously detecting the four porcine coronaviruses and the mol ratio of a primer pair is that the ratio of the PHEV to the PEDV to the TGEV tothe PDCoV is 5 to 3 to 5 to 5; the multi-RT-PCR method disclosed by the invention has the advantages that the method has multiplicity and can be used for synchronously detecting distinguishing the four porcine coronaviruses including the PHEV, the PEDV, the TGEV and the PDCoV, and in-time diagnosis of mixed infection is facilitated; the method also has specificity; the detection primer has the specificity and the detection efficiency is greatly improved; resources are saved; and the dosage of each reagent in an amplification system is saved and the detection cost is reduced.