The invention relates to a relay protection testing line for connection error proof. The relay protection testing line comprises two groups of connectors and a dedicated line. One group of the connectors is mounted on a tester and a protection device. Each group of the connectors is composed of a male connector and a female connector. Each male connector comprises a shell, a fool-proof portion and a plurality of contact pins, and is mounted on the tester; and each contact pin is sequentially connected with the corresponding voltage line or current line. Each female connector comprises a shell, a fool-proof portion and a plurality of contact holes, and is mounted on the protection device; and the contact holes are sequentially connected with the corresponding voltage lines or current lines. The other group of the connectors is mounted at two ends of the dedicated line; and the voltage lines and the current lines are in one-to-one correspondence to the connectors, and are grounded in a shielding manner. The relay protection testing line is simple in structure, reasonable in design, quick in connection, beautiful and practical, unaffected by external clutters and long in service life. Connection error can be effectively avoided, and connection efficiency can be improved.