The invention discloses a detecting device for determining a length of a foundation pile by a parallel earthquake method. The detecting device comprises a shock excitation hammer, a host machine, drilling equipment, righting drilling equipment and a trigger; the trigger is placed on a bearing platform of the foundation pile; and the host machine and the trigger are connected with a data circuit set. The detecting device is characterized in that the drilling equipment includes a drill body; a drill bit is arranged at the bottom end of the drill body, and a motor is mounted at the top end; a spiral rod driven by the motor to rotate is mounted in the drill body; and a grinding column is mounted between the spiral rod and the drill bit. The detecting device has the following beneficial effects: the detecting device is arranged as an integral structure, is fast in detection, can detect at any time without needing prepunching, shortens the construction time, and is suitable for popularization and application.