Provided is a tandem type bicycle frame testing device which is the testing device used for detecting safety performance of a bicycle in riding. The tandem type bicycle frame testing device is composed of a rear flat fork fixing seat, hydraulic cylinders, hydraulic cylinder plungers, a force sensor, middle shaft force applying clamps, bicycle frame middle shaft force bearing rods, a bicycle frame front pipe fixing rod supporting frame, a bicycle frame front pipe fixing rod, a rack, a controlling system and a hydraulic work station. The hydraulic work station is started via the controlling system so that the hydraulic cylinders apply force to the respectively corresponding bicycle frame middle shaft force bearing rods under test according to a preset force value and number of times. The force sensor transmits electric signals of force and number of times to the controlling system. When the preset force value is reached, the hydraulic cylinder plungers of the hydraulic cylinders are returned to an initial position by the controlling system and then a next cycle of force application is automatically started. When the preset number of times is reached in a reciprocating way, the controlling system instructs the two hydraulic cylinders to stop force application and instructs the hydraulic work station to stop operation. An objective of testing the tandem type bicycle frame is met by the testing device via controlling force applied to each middle shaft of the bicycle frame by the hydraulic cylinder plungers.