The invention discloses a DDN service parallel testing method, which relates to a bit error detector and at least one DDN service veneer. A first port of the veneer and the bit error detector are connected. DDN ports are established at all the ports of the veneer and the DDN transmission rate is set as the rate that the ports support and need to be tested. DDN data connection is established among the ports needing to be tested; and physical connection is applied among other ports. Thus, all the ports of the veneer are connected in serial sequence and the last port is arranged with a loop back. The method includes the following steps. (a) the bit error detector sends data to the first port of the veneer at the set DDN port rate; (b) the data are connected to the last port through data connection and physical connection; (c) the data returns to the bit error detector along the original route through the loop back arranged at the last port; (d) the bit error detector judges whether the whole route is communicated and whether the whole route has bit error according to whether data are received.