China's awareness of secure environment and war characteristics during different periods of time affects its "Active Defense" Strategy. China's "Offshore Active Defense Strategy" depends on its military buildup. China adopts multi-layer defense combat systems. Ground-Based Midcourse Defense (GMD) is to resist the enemy far away. The submarines and aircraft carriers prevent the enemy in the intermediate waters. The surface forces are deployed in coastal waters within the first island chain as the last line of defense. According to the "Area Denial" strategy in the South China Sea, People's Liberation Army Navy plays an important strategic role. It should execute the multi-layer defense tasks in the air and in the sea. The PLA Navy will integrate air force, army, and GMD to implement air-sea blockades, deterrence, and surprise attacks. The PLA Navy will play a key role to control the ground, sea, and air.