A scalable all metal reflective element is proposed in this paper, and an all-metal reflective array antenna for high power microwave application is also designed. By sliding the connecting rod up and down, the transmission path of the incident wave to each element can be changed to achieve the corresponding phase modulation. Thus, the beam scanning can be achieved. Simulation result shows that the unit can realize linear phase adjustment of 360° within 10-13 GHz and has a power handling capacity of 3 MW, which means the array can achieve 5 GW/m² power handling capacity level after the formation (under vacuum condition). Under the standard of 3 dB gain variation, the antenna can realize a two-dimensional spatial beam scanning within the range of 90° revolving cone angle.