The utility model relates to a three-phase electric power parallel connection device and a relay protection test system. The parallel connection device comprises a first three-phase connecting line, asecond three-phase connecting line and a connecting piece. The first three-phase connecting line and the second three-phase connecting line are respectively provided with an A-phase line, a B-phase line, a C-phase line and a zero line. The connecting piece comprises a first plug, a second plug, a third plug and a fourth plug. The first end of the A-phase line of the first three-phase connecting line is connected with the first end of the A-phase line of the second three-phase connecting line, and is connected to the first plug for external plugging; the first end of the B-phase line of the first three-phase connecting line is connected with the first end of the B-phase line of the second three-phase connecting line, and is connected to the second plug for external plugging. The first endof the first three-phase connecting line C phase line is connected with the first end of the second three-phase connecting line C phase line, and is connected to the third plug for external plugging.According to the utility model, the work of a parallel voltage loop can be saved for a tester, and the risks of false wiring and false touch are reduced.