Destructive accident sometimes takes place though the equivalent stress is rather low in the viewpoint of strength of materials. The propagation of fatigue cracks under multi-axial stress state and cycling load gives the reason. Fatigue fracture has been considered as one of the most commonly encountered industrial problems that lead to the damage of components in engineering products. In general, the machine structure is always under stress concentration or stress cycles. Moreover, the structure material is usually under two axes or multi-axial stresses instead of uniaxial stress state. It is important, therefore, to clarify the propagation behavior and the fatigue failure problem of the crack under the multi-axial stresses and cycling load from the safety reliability and accident prevention measure. In this study, a biaxial fatigue experimental device was developed which can carry out a wide range of fatigue tests under biaxial stresses. The developed experimental device was identified with a biaxial fatigue experiments including static uniaxial and biaxial tensile test by using the aluminum alloy flat plate as specimens. The propagation behavior of fatigue crack for center notched cruciform specimen in the equal biaxial fatigue test was verified.